This issue with switching chars and crashing reminds me of legacy ender client crashing in a similar way.
To fix legacy ender client crash (because it would keep crashing every time w that char until -) I had to delete the "belt" files . belt files being the hotkey saves for icons (like dig, lift ect) . Only then could I log in a char, I used to get salty cus I had to rehotkey stuff unless I had them backed up.
I guess its different because with amber client I just crash that one time and changing nothing I just restart client and am ok to log in. but Maybe its somehow related, specifically the way hotbars are saved for chars?
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Also thinking now it might be if you log in on a char (billy) and then switch to a diff char (bob). When you go back to billy is when it crashes maybe. just trying to trouble shoot a bit
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concerning the crash on logout, could it be the ctrl + M feature being left on while switching chars? Since it deals with account status ect.