MMA video series artwork disappeared after update MMW and sync

[HSD]

Hi,
I use MMW primarily as a video library (MP4), not for music (MP3).
My collection includes many clips, training videos, and especially video series, which I manage in MMW and sync to my Tablet with MMA (Beta).

After updating to MMW 2024.2.1.3210 (portable) and syncing to MMA (2.1.1.1290), all of my video series thumbnails disappeared in MMA.
To clarify: this issue does not affect the thumbnails of individual video files.
It affects the series thumbnails that MMA normally displays for each video series.

What I tested:
After extensive testing with different tagging setups in MMW, I observed the following:
I tried tagging the files as music
I tried tagging them as videos
I removed almost all tags except Series Title and Artist
I tried simplified and mixed metadata
I synced small batches and full batches
--> No matter which tagging approach I used, after syncing, no series thumbnail appeared in MMA.
(I tried both USB and WIFI sync, with same result).

Temporary workaround
The video series thumbnails reappear sometimes (but not reliably) when I rename or delete the Album Artist or Album fields directly in MMA.

Additional issue:
When the series thumbnail finally appears after this workaround, the quality is extremely poor.

Previous behavior:
With older MMW versions, I had occasional thumbnail issues, but after several sync attempts and transferring smaller batches of files, the series thumbnails eventually appeared.

With the new update, they never appear automatically anymore.

Any idea how to fix this?

Thanks for help!