I’m expieriencing a similar issue on two self hosted nextcloud servers (both running in Ubuntu 20.04.1, one installed a snap, the other “manually”. Version 20.0.1, Client version 3.0.3 (Windows 64 bit).
It just says “wait” in the client (no matter if Windows, macOS or Linux, no matter if over internet or in a gigabit LAN).
Pretty anoying actually. Especially if you consider, that nextcloud discourages the use of it’s internal encryption module and other products like seafile have encryption available by default. There you can also open encrypted files in the web interface by a set password.