Hello Cayleen and sorry to hear you've encountered such a nasty issue.
I really can't think of anything that could've caused this except some Steam cloud sync issue, but there is a few things you could do to try to get your save data back.
First thing to do is to check that you are using the correct save slot. From the games main-menu go to Settings -> Save Slot and check that you're using the right slot. If every save slot appears empty read on.
Check that the actual save files still exist in Steam/userdata/[your_steam_id]/35720/remote .
There should be files named something like "slot1_v119" / "slot2_v119" among some options files.
The files starting with "slot" are the saves the first number idicating which slot it is. The second number states which version of the game the save is used for.
If the files still all exist, backup them to a different directory.
Test what happens if you disable steam cloud sync for the game. You can do this by right-clicking Trine 2 in your Steam library and select properties. From the properties menu select "UPDATES" page and uncheck the "Enable Steam Cloud synchronization for Trine 2". The game will now use your local saves instead of the ones in the Steam cloud.
Its likely that the above alone won't make a difference, but its worth a shot. The following won't probably bring 100% of your progress back, unless the save data vanished right after an update: while still using local save data check if you have multiple versions of the save slot you're trying to get back (the more recent below the current version, the better). If you do delete all the files that have the current version (you did backup the data right
) including options and slot files (ie delete all v119 files and leave everything else). Now start the game again and it will try to generate v119 saves from the older ones. As mentioned if you've played a lot on the current version this will not bring that porgress back.
If none of this help please give us some more details how this happened like
-Did the issue occur after updating the game or just all of a sudden
-What operating system are you playing the game on
-Are you playing on multiple machines, or just one
Any details you can remember can help us track down the cause.
Really sorry for the inconvenience and hopefully we can get your saves back!