reproduced on 1.15.2 and 1.16 snapshots by multiple people(3 dutch, 1 finnish, others) over multiple mc vanilla mc servers with different maps at multiple hosting providers (hetzner and OVH)

Players sometimes get disconnected instantly on join. Or it works for about 20 seconds normally. Then for 30 seconds you sort of "time out" where nothing you do is visible to others or the other way around and then you get a connection closed by remote host.

I believe this is not a bug on the client end given how many times i have seen it (more than 10 times on different unrelated servers and people). I hope you could take a look

The servers just sees a disconnect message as if a user disconnects manually.

These clients are on totally different ISP's and not using VPN services

server displays:

[13:56:47] [Server thread/INFO]: madragon lost connection: Timed out

client sees: