Cryptomator needs a locally accessible file system. It is not aware that you’re using WebDAV, i.e. it doesn’t know or care whether it is mounted via dav
or davs
.
I am not sure if it works 100% fine with vaults located on a GVFS WebDAV mount. Ironically the unlocked vault provided by Cryptomator itself uses the very same technology. This will change with the upcoming version 1.4.0, which adds FUSE. If you’re interested check out the beta. But the storage location of the vault will still need to be a locally accessible file system, so your problem will most likely not magically disappear.
There is a bug in the .deb installer, which is missing the log configuration. This can easily be fixed, see this answer: