I see what you mean. We should probably do that. Would you like to submit a PR?
Ok, sorry that --webdav-auth-redirect didn't fix it. My best guess would be that OpenCloud is not fully supported at the moment. I note that there is an open PR to add it here:
You might consider building that branch and seeing if it works better for you. (I am not the author and cannot vouch for its security or effectiveness.) If you still encounter the error, you might consider reporting it on that PR thread so that the author can address it. Presumably they will be more familiar with OpenCloud and have a better idea of what's going on.