How many did you have enabled at once? Up to 15 should be safe. I’ve heard of problems starting at 18, but the exact upper limit may vary for each user/PC. Let me know how many you can get going at once. Item-heavy Add-Ons might consume more RAM than tile-heavy ones.
Here is the list of Add-Ons I can get it to run with and their corresponding KBs of data:

Alex, that’s almost certainly because you have too many Add-Ons enabled. See the last part of this Kickstarter Update.