Thanks for your response. I think I can reproduce the issue so will try to describe below. The issue appears to only happen when I have previously opened a vault with a pre-assigned drive letter. After I do that then I can not open a 2nd vault and get the error 85 in the log file.
In my case I have 8 vaults, but I don’t think the quantity of vaults makes a difference.
If I setup all my vault with non-assigned drive letters, I can open up all 8 vaults one after the other and Cryptomator will assign consecutive drive letters starting with Z:, So Vault 1 = Z:, Vault 2 = Y:, Vault 3 = X: etc. So no problem here.
Now I assign 1 vault (it does not matter which vault) a pre-assigned drive letter, say drive letter T: I then open this vault with Letter T:, no problem here.
I then try to open the another vault and it fails to mount. It will unlock but just not mount. Now I get the error “Connecting drive failed” and error 85 in the log file. So here I can not have more than 1 vault open at any time because each successive vault fails to mount.
If I close the vault with letter T:, I can then open any other vault (with un-assigned drive letters), but it will mount with drive letter T: (as oppose to Z: as default). But now I can not open my vault with pre-assigned letter T:, because now T: is in use with another vault. I think this is a problem and should not happen. I think Cryptomator should not open non-assigned vaults with letters from pre-assigned vault. Something for you to consider.
Also now I can not open any other vaults. All other vault fail to mount.
So from this point on, every vault which I open, opens with T: and I cannot open a 2nd vault.
To solve this, I have to shutdown Cryptomator and restart it. This seems to flush the memory of using T: and then all vaults can open as described in point 1 above and all is again well until I open a vault with pre-assigned drive letter.
I also run Mountain Duck to mount drives sometimes, not permanent, just off and on. I thought there maybe some conflict there but it appears not to be any conflict. Cryptomator avoids using drive letter already mounted by Mountain Duck. For example, if Mountain Duck mount a volume with drive letter Z: (which Cryptomator uses as first choice), then Cryptomator will avoid that letter and mount on letter Y:
Also I don’t or do anything special to my setup. It is essentially a standard windows 10 pro installation with default settings. I do not go tweaking things.
I hope you understand my description and that you (or somebody else) can reproduce it, as I would really like to get off the “rare issue” list.