Manual saves are being deleted by the game for some reason. Only the 4 most recent saves are being retained. Two of them being auto-saves which are incorrectly marked as Manual Saves. I still have saves from 2017, but Beta 1.0 is deleting (or rather, overwriting) only between 4 save slots from newer versions of the save, even if you save manually or quick save.
I was doing a 100% achievement run for the new achievements with Hidden Hat, Pizza and Gas Cylinder, but I lost the saves 
The save filename counter appears to be broken. The first save is correctly saved as bms-000.sav, but the next save gets saved as bms-0-1.sav, and all subsequent saves get saved as bms-0-1.sav, overwriting the last save.
The bug is only present when using the new UI. You can launch the game with the -oldgameui launch option to use the old UI, which doesn’t appear to be affected by the bug.
Alternatively, you could increase the save_history_count convar in order to increase the number of stored quick and auto saves (for example, put save_history_count 10 in autoexec.cfg). The default value is 1 which will keep one quick save in addition to the most recent one.
If you are doing achievements, keep in mind that 1.0 final will be released on March 5th, which will break your current saves. Also, some of the achievements are reportedly bugged in the current beta, which will be fixed in the 1.0 release.
A new beta was published a few hours ago (https://steamcommunity.com/games/362890/announcements/detail/1716372790325903245). Unfortunately, the bug is still present in the new beta. I’ve reported the bug on the official discord server.
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