Just an update... It seems that there is no Proton 3.16 folder in my "common" folder. There is however a Proton 3.7 folder. So it would seem even though i have selected to use the newer version of proton the steam client has not downloaded it.
I've tried changing to beta client and changing proton version multiple times but it never seems to download the newer proton.
Is there a way i can force it to redownload the proton files?
Try verifying the integrity of your game files with Proton 3.16 selected in settings. This triggers Steam to check the Proton files as well.
Unfortunately this doesn't seem to be possible to do for Elder Scrolls Online, as it is "greyed out".

It looks to me like something is very wrong with your steam installation. It might be worth trying a complete uninstall/removal of Steam and reinstalling it to determine if this is a fluke or if something on your system is triggering this failure consistently.
Already tried completely removing steam AND the game. Same results, newer version of proton doesn’t download.
I don’t fancy removing the game and steam again as it’s almost a 100GB download.
I have however done some more testing and found that if i download another game (i bought a cheap game for testing) with proton 3.16-4 enabled. It WILL then download 3.16-4 for that game and then work.
So it seems that steam itself is not downloading proton purely based on the setting change. You'll need to download a game to get the newer proton and it will not install a newer proton to an already installed game.
Seems like this could be something that can be easily fixed. I have also noted if i REMOVE the new game it'll also remove the proton associated with the game too, bringing us back to square one.
Validating game files and downloading depots, including Proton is managed by the Steam client, which makes this sound like a Steam client issue. Let's track this issue on Steam's side for now.
Agreed, it does seem like a steam issue and not a proton one.
I’m wondering if this is unique to Elder Scrolls Online? In so far as Steam only really downloads a launcher and base files and the games launcher is where it actually updates itself... Not via steam updates.
Maybe this is why I can’t verify game files in steam and why proton doesn’t seem to change version or update....
Let me know if I can provide any more information to help with a fix?
Thanks.
Hello @Yorper, per "Fixed more instances of 0-byte downloads and missing Proton or data files for Steam Play titles" in the 2019-03-06 Steam beta client update, please opt into Steam's beta client if you are not already and retest this issue.
Sorry for the late reply.
After changing to the latest beta client and changing in my settings to a version of proton not currently installed. I can now confirm steam client downloads the new proton version selected and everything works as expected. I would say this issue is now resolved.
Thanks for your work.
I still have the very same issue,
using steam on arch linux with i3wm. if i download a new game it will download steam 3.16.8 beta but otherwise it wont and im getting the exact same errors described on this report.
I am opted into steam beta
proton 3.16-4x2 2018-12proton 3.16x2 2018-12proton 3.7x1 2018-12
_Originally posted by @kisak-valve in https://github.com/ValveSoftware/Proton/issues/556#issuecomment-447582158_
As requested...
With the new proton 3.16-4 and 3.16-5 beta i can no longer launch Elder Scrolls Online. This is the only game i play with proton so i cant test any other games. (TESO works pretty well on 3.7-8 though).
This is the error message when i try to launch the game (with steam started from terminal).
This is the system spec of the running machine...