Plugin limit problem,slot remains empty upon loading

there is a limit of plugins that can be used in a project and it’s not vendor related…
UAD,Waves,Brainworks…doesn’t make a difference…

Actually it is somewhat vendor related I think.

Regularly see posts where people say I know it’s not cpu related because I can’t even load UAD plugs etc, etc.
The only other plug I’ve seen blamed was Omnisphere (but guess what…that poster said that with Omnisphere open he couldn’t load his UAD plugs)
So as far as I see UAD is the common denominator here…or UAD in combination with Cubase at least.

Medway Studios…UAD on your system??