Hi @Torsten Berning
Can others open the (2020).vsd file properly?
Does the (2020).vsd file come from the location same as (2018) .vsd file?
I suggest you use 3rd-party software to open and check whether the file is corrupt. Such as LibreDraw.
Besides, I find a similar, you may try purplegerbil's suggestion.
https://visguy.com/vgforum/index.php?topic=7166.msg41134;topicseen#msg41134
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