In addition to my Slingbox M2, I discovered that streams from Plex to my Roku 3 would occasionally crash. I did a quick search on "Roku 3 version 7.7.0", and discovered quite a few people were having problems with various streaming apps (Plex, Netflix, etc.). Because I had been out of town for a few weeks, and I purchased my M2 around the same time the Roku 7.7.0 was released, I didn't realize there was a new version, nor did I have an opportunity to try the M2 with any other Roku release.
I found instructions for accessing the "Roku secret settings" screens, and was able to downgrade my Roku 3 to 7.6.0 build 4125-04. After three attempts, the M2 seems to be streaming to my Roku 3 without a problem so far.