Patrice: I had a similar problem. It was something unrelated to Maple in my case. I use Maple on a Macbook Pro. While using it, the whole system froze up and could only clear it by restarting the Mac.

In your case, it may be something causing memory pressure or hogging CPU time. In my case, it was iCloud uploading/downloading (bird) and spotlight indexing {mdworker} running simultaneously. The processer(s) were on their knees.