I’ve never seen an error like that myself. Searching the web for that particular error code shows a wide range of different possible reasons. Some involve incorrect server configuration, some indicate Cloudflare issues, some claim that the problem is on the client side (notably web filters and proxies can cause issues).
If this is something that can be fixed from our end, I’d love to do so. But I have no idea what the issue is or if we can even fix it at all.
I’ve seen a couple of ERR_QUIC_PROTOCOL_ERROR myself (not the file manager though), this happens to me because the QUIC protocol works over UDP and some ISPs may not prioritize UDP packets so they drop way more than TCP, sometimes so many where the QUIC connection simply fails