Hi Big K,
I use a SmartAV Tango control surface which does require a lot of devices to be added in Nuendo, but a few updates back I was able to install all required devices and still add a fair number of inserts to a project, but now it is impossible load them all and the number of loadable plugins into Insert and Send slots has been much reduced. The project that I am currently working on has only 45 tracks in total (all types - audio midi sends etc.) and only 15 plugins, and already it struggles when I try to add another plugin. Sometimes the plugin will simply not load or sometimes I will just get a blank plugin window. To solve this I have to remove some SmartAv devices in Device Setup thereby reducing the number of audio tracks at my disposal. This gets worse with every Nuendo update - while nothing changes at my end (no changes to SmartAv).
There are others here who have reported similar issues and they are not all Tango users, so the problem does not solely relate to the Tango.
On Windows operating systems it is only possible to install a maximum of 256 DLL’s or Plugins, however this limit is dramatically reduced by Steinberg DAW’s and in my experience the number installable seems to be reduced with every update.
Here are some previous posts that relate to the issue: