That's been a long time issue on Boost for Reddit as well. Boost doesn't save its state properly when the activity gets closed, so you get a cold start. Some phones are bad and just kill it outright, but the good ones gives the app an opportunity to save its state.
I usually see it after using multiple heavy apps after Boost, immediately after is a bit weird unless it's a really low end device that just doesn't have the RAM to keep any activities open in the background.