every time archicas saves it creates a scratch file first. I could be wrong but then does something like this; When all is hunky dory it changes the name of your file to the backup and the scratch to the name of your file. ( deleteing the bakup in the process.)
I have found during a faulty save process the scratch can get left.
Did you crash during a save process?
I think it is better now but there was a time scratch files where created in the cache folder and never deleted, resulting in a gigabyte sized folder.
On mac look in library/cache/graphisoft/AC v8 etc and you might find a few too many scratch files which can be happily deleted.
Cheers John
John Hyland : ARINA : www.arina.biz
User ver 4 to 12 - Jumped to v22 - so many options and settings!!!
OSX 10.15.6 [Catalina] : Archicad 22 : 15" MacBook Pro 2019 [/size]