Selectively suspending threads is a good feature, but be warned that it can cause arbitrary deadlocks, which won't be possible otherwise. Eg. it's possible to suspend a thread in a synchronised method and then the other thread will just block.
That is not a deadlock. That's a paused thread a running thread is waiting for. If you unpause all the threads again your program should continue as usual. If not then you have some fun debugging of race conditions ahead of you. (Ignoring time outs and watch dogs)
The main PITA is that multithreaded debugging in IDEA is awful: it is not possible to suspend all threads and resume only one thread.
In spite of the "Improved debugger" it seems that this problem is not fixed in v14: https://youtrack.jetbrains.com/issue/IDEA-43728
:(