PNG coverart no more readable from amplifier and car

Hi all,
after I don't know exactly from which version of MP3Tag, my Onkyo amplifier and my Audi A5 too won't read anymore the coverart embedded if I use the function "Adjust cover art"
The resolution is correct (800x800), the format is correct (PNG)...but the coverart won't appear anymore during the playback.
If I use an old file with readable coverart and I use the function with the exact same resolution and format, the coverart become unreadable.
Any idea?

Does it make a difference, if you choose the format "Original" instead of PNG?

Does your Onkyo and A5 expect (and show only) PNG in 800x800?

Have you saved the cover to the file system and checked whether the image is OK?
And if the image is OK, have you embedded the picture again and checked what the player does?
Have you tried to export a png from an old file, delete the cover art in that file and re-embed the picture and then see whether your players show them or not?
Could you supply one of the files with an unread image?

No, I tried some minutes ago and the problem is the same. Original file has coverart visible. If I "edit" and save it with MP3Tag...the coverart are no more readable. It is a recent problem, I've done more or less 1 TB of files before and no one problem.
Audi entertaiment system has a limit of 800x800 PNG file, I don't know nothing about Onkyo limitations.
A clarification: if I use a Windows player, like AIMP, no problem with the coverart embedded.
Thanks for the help

Yes, if I save the image the file is readable.
If I use the image saved, the coverart is not readble anymore.
One file, generated with the actions you suggested me is in attach. is called newone.flac. The old, and readable one, is called oldone
Thanks a lot

I can't find any difference for the PNG-Part in the two provided FLAC files. The picture part seems to be identical. There are some small differences in the metadata part, but this should not affect the cover art:

Thanks @LyricsLover...I repeat just to be clear: no problem with Windows player or Kodi...just with Onkyo embedded player and Audi too

I only find this change with respect to FLAC files in the changelog:
[2021-06-30] CHG: VorbisComment block is now always written before Picture block for FLAC as a workaround for an issue in Windows

So if you can find files that work and have been written after V3.08 and June 2021 then it has nothing to do with this change.

As apparently the behaviour is hard to reproduce for persons who do not have that kind of Audi (on a side line: "Audi" fascinatingly comes from the old company "Horch" which means "Listen!" - I don't know their opinion to "see" things...).

Is there any other more common player around that you know to show the same behaviour?
I mean, both manufacturers might have issued firmware updates that made things stranger.

How do the players cope with jpeg or pictures that have a little smaller dimensions like 790*790?

You see me shooting in the dark.

Thanks for your time.

I can try with BMW player as soon as the new car is arriving home...
With Jpeg embedded coverart it never functioned.
Do you know if there's a way to have old version of the MP3tag installation file so I can try with them?

I'm not sure about the reliability of this website, but they list different older versions, including the v3.07 and v3.08:

Great, thanks.
I will try with one or two and keep you guys updated.

Ok, I've gone through all the version to 3.12...nothing changed.
Maybe is better for me to focus on something else.

An update: if I copy the file from the NAS to an USB stick...it wokrs with the Onkyo amplifier. So maybe is something related to the way the NAS exposes the file...or the indexing of them.
Feel free to consider the problem solved. Thanks to all

The difference could be that if you plug that USB stick directly into the amplifier then that reads the folders and really the files.
If you access the files via the network on a NAS, you may access a DLNA server that may have to be configured to also transmit pictures.
And it could be that the DLNA server stll has to update its picture store so that after a while you will see the picture (just guessing).
I don't know how you got the audio files to the car stereo - but I would consider that problem to be something different. Perhaps that player expects a picture file in the same folder. Maybe you have to check for hidden files.

Hi all,
the final resolution: the problem was the DLNA server on QNAP, the integrated one: it was not rendering anymore correctly the coverarts. I disabled the integrated DLNA server and install Minimserver: all working now!

Thanks to all for the support

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