Something I noticed with 1.5 under Ubuntu 18.04 with a dual-screen system.
I just purchased so I was googling on one screen under firefox for help, while playing on the other, I noticed that my firefox would become non-responsive. Exiting flowscape fixed the issue.
I have 16G of memory. I've attached lshw output if that is helpful. If I can grab a tty via xterm or SSH while using the app I can run any program to provide any info if so interested. I also could be running out of swap. I have only 2G of that and I do see high usage of 16G while running.