Extremely short answer.
Start the terminal - and run a command like this:
sudo purge
Enter the administrator password.
At this point, there will be a RAM cleanup - and if the Blox was lagging or its icon turned into a dot - it will all go away.
Start with a simple restart of BLocs - but I have repeatedly encountered that this does not help.
For example - in a huge project - stop adding photos. At all.
Restarting Blocs - the situation does not change.
Run the cleanup as I wrote above - everything works again.
This thing is absolutely safe for the device as far as I read. The only thing I recommend is to turn off the music when you start it)
PS: I work on a macbook pro 15 2018 - i7 8870H 16 gb RAM radeon pro 560x. And frankly speaking Blocs slows noticeably even with simple operations - sometimes comes to such problems described above.