1. Disable clients' sprays
2. Set your clients' cl_dlmax to 96
3. Set your clients' cl_download_ingame to 0
4. Set your server's mp_logdetail to 0
5. Set your server's sv_timeout to 42
6. Disable all plugins that manipulate radar or change players' models (if they use other method of changing models than the so called ZombiePlaque method) or add extra items to HUD.
May help or may not. Without this, our server was plaqued with svc_bad; now it is the distant past, or maybe because I no longer play on my server and do not notice those errors?
No, just joking.
Anyways, it worked for me (after many hours of googling and searching for a solution to the problem).