Can’t back-up theme

Hi there,

I wanted to do a backup of my site. Normally I use Updraft Plus (Version 1.16.47). But whenever I tried to do the backup just now the log file says this:

0007.351 (0) Beginning creation of dump of themes (split every: 800 MB)
0007.361 (0) /homepages/8/d20921870/htdocs/wp-content/themes/AdvanceImage5/functions.php: unreadable file
0007.369 (0) [Warning] themes/AdvanceImage5/functions.php: nicht lesbare Datei – konnte nicht gesichert werden.
0007.372 (0) /homepages/8/d20921870/htdocs/wp-content/themes/AdvanceImage5/header.php: unreadable file
0007.379 (0) [Warning] themes/AdvanceImage5/header.php: nicht lesbare Datei – konnte nicht gesichert werden.
0007.391 (0) Total entities for the zip file: 98 directories, 410 files (0 skipped as non-modified), 9.5 MB

(the German parts just repeat that the file isn’t readable and couldn’t be saved)

I then got a new backup plug-in called WPBackItUp (Version 1.40).
Here it too encounters an issue with the backup when coming to the theme. Here’s the log for this:
Preparing for backup…Done
Creating inventory of files to backup…Done
Exporting database…Done
Backing up database…Done
Backing up themes…Failed
Backing up plugins…
Backing up uploads…
Backing up everything else…
Validating backup…
Finalizing backup…
Error: (120) Unable to backup your themes. Please try again

The theme has just been updated to Version: 1.9.0. My WordPress is also updated to Version: 5.6.1.
Is anyone able to tell me why I cannot backup the theme? Would it be an idea to skip the backing up of the theme and just backup the rest?

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