I have a server that is extremely slow (takes 3-5 minutes) at starting X11 applications over a forwarded X11 link. I have tried connecting to it with 2-3 different machines with different operating systems. After the applications start everything seems to be fine. I am connecting using trusted X11 forwarding (ssh -Y) and using cert based authentication (not that that should matter).
The operating system is Gentoo Linux on amd64. None of the applications give any messages related to the X environment (one shows nothing, another just a standard welcome message and the last an error message about a resource being in use (which the window that finally popped up told me about as well).
As per Bertera's suggestion I ran with the -v option. It doesn't print anything until the window shows up when it prints:
debug1: client_input_channel_open: ctype x11 rchan 3 win 87380 max 16384 debug1: client_request_x11: request from 127.0.0.1 43716 debug1: channel 1: new [x11] debug1: confirm x11
Also, I have tested ssh port forwarding and it is extremely slow as well (and I'm guessing this could be the problem with the X11 forwarding).