Hi Stefan,
This problem has been reported twice before and so far I could not reproduce it and solve it.
For the other users it appeared that the problem occurred when they migrated to PHP 8.
And when they went back to PHP 7 the problem disappeared.
On the web I saw that many other people with different applications are having this same problem.
Are you using PHP 8? and if so, could you go back to PHP 7.4 and try the Restore again? and let us know your findings.
Roel