I encountered a bug about 14 hours into an Endless Run where, after exiting a location and getting into my raft, I'd immediately sink below the surface of the river and then fall forever. The problem persisted after reloading the save which indicated something in the save file was broken. I looked around online and saw a few people who had encountered this, all of which resulted in them needing to start over. I saw some posts from the devs saying they were looking into it but since it's 2023 and the bug still occurs, I can only guess they never figured it out.

Since the prospect of losing 14 hours of progress would have made me uninstall the game, I decided to poke around in the save file and see if I could massage whatever the broken values were into something workable. After about 4 hours of tinkering, I managed to spawn myself in the air, which then had me fall back into the river where I was able to continue on.

This is a pretty easy fix to do, all things considered, so if you've found yourself in the same situation as me, the following guide should get you into a state where you're able to continue.

First things first, go find your broken save, which should be located here:
C:\Users\<user>\AppData\Local\RiverGame\Saved\SaveGames\SaveGame.sav

Now, go to your favorite hex editor. I used this one online (it's free): https://hexed.it/
Open up the save file in the editor and do a search for "PlayerPos". Mine was basically at the bottom of the file. You should see something like:
PlayerPos.....StructProperty.............Vector.................<some hex characters here>05 (05 is final hex character and marks the end of the sequence)

There's 12 bytes of hex characters, 4 bytes each for the X Y Z values of your character's position. The last 4 bytes represent your character's vertical position. Because the bug is your spawn is just below the river, we just need to bump up your vertical height a tiny bit so you don't get stuck. So just change the final byte to a slightly higher hex value.

As an example, my vector sequence looked like this:
2B 25 BB C6 0F 2F AB C7 8A 11 DC 42
2B 25 BB C6 = X value
0F 2F AB C7 = Y value
8A 11 DC 42 = Z value
All I did was change the final byte of the Z value (42) to be slightly higher (44). Then, save the modified hex and you should be good to go!

Load back up your save file and you should spawn in the air, then fall back into the river allowing you to continue on.