For a while REAPER has been crashing often when I insert a plugin. This is NOT normal behavior and not what I am used to seeing. After a dozen crashes this morning I stopped trying to mix and tried to figure it out.
Clearing the plugin cache didn’t help and neither did installing the latest update. Eventually I found a preference that I normally have enabled was actually disabled. This option is called ‘Bypass audio while opening plug-in config window‘ in the Plug-ins>VST settings.
The good news is REAPER doesn’t crash anymore, the downside is playback glitches momentarily when inserting a plugin or opening the UI (which is the reason I disabled it before).
If REAPER is crashing often, give this a try.

@sk4ggs Hello, is REAPER still crashing a lot? This might help. Check out the latest on the blog http://t.co/BKGe4L87
Yeah, I saw your tweet yesterday about that. Hopefully there will be a fix soon.
The momentary glitch isn’t really Reaper’s fault in that they’re having to work around buggy VSTs. I assume most DAWs are similar in that they are likely to crash with those VSTs unless they have a similar workaround?
It was pretty random which plugins would crash during playback or stopped. All 3rd party, some Waves, some Slate Digital, and others. Enabling this option fixed it and it was solid for the rest of the day.
It wasn’t that long ago that Pro Tools got the ability to add plugins during playback, and yes there is a momentary mute, often a long moment, often a long silence as the whole computer crashes.