This will indeed likely be a single plugin causing issues, its just that cache is in play too. So you would need to disable all, clear cache and ensure its working, then enable one at a time, clearing cache each time if you have an issue. The reality is there, with the amount of plugins you are running, you are going to run into issues at some points unfortunately. Just for an example, every time someone visits a topic at present, there is an error thrown, and there are 32 hook items being loaded at that point. Any one of those could be causing your issues.
With the support. Support has changed on the platform, and this is indeed where you would post up for support. We still have access to your system, and this is now fully staffed. We can move items into email support if there is an issue which requires more secure information, or requires the item to be escalated to higher tiers of support