Befuddling Whole PC backup behavior after adding the 2nd drive

I am using ATI 2020 but the "old" .tib format to home NAS. I must keep the old format for reasons urelated to my question.

The drive C: is a 512 GB in an NVME slot. I added an internal (but not on-board) SSD drive D:, 2TB. When I did the first backup after adding the drive (full, of course; I installed the drive so that it fit my backup schedule), the progress indicator showed an enormous time, about 15 hours (although the added drive was empty, and has only 1TB allocated as a GPE partition, rest being a reserve), although previously full backup time did not exceed 3 hours (LAN-bound, I have only 100MBps in my home office). I shrugged and let it go. The backup completed in ~3 hours, although I did notice the progress bar did not move for a very long time. I shrugged the problem off: as long as it backs up data, I do not care.

After the 2020 Update 3, the things became even more interesting. The Recovery / Files tab shows an empty drive D:, as if there were no files on it. The Recovery / Disks and Recovery / Partitions tab do show a 1.8TB disk with a 1.0TB partition on it. However, on the Recovery / Partitions tab the disk label is shown as "Local Disk (D:) 1 TB", although the real disk label is "DATA", and shown by Explorer. The C: backup does show the correct label, however.

The same drive in Explorer has a label

And the Recover / Files tab shows an empty drive.

Indeed, an attempt to restore D: to an alternative destination on C: has completed instantly and resulted in an empty directory.

I never had to change my script file by hand, as I upgraded from ATI 2018. Just in case, posting it redacted at the very end.

There is not much unusual about my configuration: Windows 10 Pro build 19041, ZD370 HD3P motherboard from Gigabyte, the drive D: is on an Intel chipset channel. Something of note is a bit tightened security, as I have someone else's data (it's my work), and I always treat someone else's data as sensitive and never judge whether they really are. So secure boot is on on this machine, although I neither perform measured boot or encrypt drives; also, the enhanced kernel memory isolation is on (this is available through policy only), plus all the checkboxes in Windows Security panel; this is what I've got at the end. Tighter than many people use, in my experience, but far from being turned up to eleven:

Is this a known problem with a known solution? Thanks!

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ADDED 2020-10-20. I decided to back up drive D: separately and exclude D:\ from the full backup. ATI does not think that the partition has a filesystem on it!

Windows Disk Management indeed disagrees:

I also tried repair reinstall, to no avail. I do not know what to do and what to try next. To say I'm desperate is to say nothing.

The only place that does show the realistic total size of the backup is the Recovery / Files, when My computer is selected. The same page shows an empty D: drive (note the "–" indicating the expanded tree).

I confirmed that both drives have a GPT.

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The script is below. Everything in square brackets indicated a redaction or removal of irrelevant, as I believe, information.

<batch>
  <version>1.0</version>
  <uuid>[UUID_1]</uuid>
  <display>OMEGA</display>
  <priority>low</priority>
  <stage>
    <before>
      <user_command><command enabled="false" /></user_command>
    </before>
    <operations>
      <backup check_after="false" notarize_files="false">
        <reserve_backup_copy format="tib" need_reserve_backup_copy="false">
          <volume_location partition_id="" uri="" volume_id="0" />
        </reserve_backup_copy>
        <antivirus_check_common_options default_action="abort" enabled="false" scan_archives="false"
                                        scan_boot_records="true" scan_cookies="false" scan_mail="true"
                                        scan_no_heuristics="false" scan_not_recursive="false"
                                        scan_processes="true" scan_programs_only="false"
                                        scan_registry="false" try_update="false" />
        <media_builder_options destination="" enabled="false" />
        <archive_options check_network_timeout="false" computer_id="[UUID_2]" format="tib"
                         id="168550514426209985" network_timeout="0" split_archive="false">
          <volumes_locations>
            <volume_location partition_id="" password="[PASSWORD_1]"
               uri="nas://[REDACTED]/OMEGA_full_b5_s1_v1.tib" username="[USERNAME_1]" volume_id="3942923557" />
            <volume_location partition_id="" password="[PASSWORD_1]"
               uri="nas://[REDACTED]/OMEGA_inc_b5_s2_v1.tib" username="[USERNAME_1]" volume_id="664174797" />
            <volume_location partition_id="" password="[PASSWORD_1]"
               uri="nas://[REDACTED]/@task@.tib" username="[USERNAME_1]" volume_id="0" />
          </volumes_locations>
        </archive_options>
        <common_options allow_multi_volume_snapshot="false" allow_reset_archive_bit="false"
                        app_settings_backup="false" chassis="3" description="" entire_pc="true"
                        exclude_by_mask="true" exclude_hidden="false" exclude_system="false"
                        execution_count="51" fast_incremental="true" ignore_encryption="false"
                        increment_type="incremental" nonstop_backup="false" ocb="false" rotation_count="7"
                        rotation_scheme="1" skip_security="false" smart_backup="false" snapshot_mode="vss">
          <file_mask pattern="$Recycle.Bin" />
          <file_mask pattern="*.tib" />
          <file_mask pattern="*.tib.metadata" />
          <file_mask pattern="*.tmp" />
          <file_mask pattern="*.~" />
          [MANY SIMILAR LINES SKIPPED]
          <file_mask pattern="D:\NOBACKUP" />
          <stream_options allow_silent_media="false" cache_network_write="false" compression_level="maximum"
                          encryption_algorithm="none" format="tib" freespace="0" ignore_bad_sectors="false"
                          reattempt_count="5" reattempt_on="true" reattempt_pausesec="30"
                          silent_asz_cleanup="true" silent_mode="false" type="disk" ver="1">
            <net_speed_limit speed_limit_mode="kilobits" value="0" />
            <disk_speed_limit speed_limit_mode="absolute" value="0" />
            <traffic_quota_limit traffic_quota_limit_period="month" value="0" />
            <quota age="110" scheme_flags="18" type="2" />
          </stream_options>
        </common_options>
        <disk_source has_asz_backup="true" sector_by_sector_backup="false"
                     sector_by_sector_backup_unallocated="false">
          <holder strid="\local" />
        </disk_source>
      </backup>
    </operations>
    <after>
      <user_command>
        <command enabled="false" />
      </user_command>
    </after>
    <after>
      <user_command>
        <command enabled="false" />
      </user_command>
    </after>
  </stage>
  <silent-reboot>false</silent-reboot>
  <common_options>
    <silent_mode enabled="0" />
    <notify>
      <email address="" authentification="false" enabled="0" [CLIPPED-NOT INFORMATIVE] >
        <notify_mode full_log="true" operation_complete="true" operation_fail="true" operation_message="true" />
      </email>
    </notify>
    <show_only_own_task enabled="0" />
    <shutdown_after do="0" />
    <force_shutdown do="1" />
  </common_options>
</batch>

Convention: UUID_1 is not same as UUID_2; PASSWORD_1 is same throughout.