I've been using Linux for a long time, including chromebooks, and this sounds like textbook low memory to me. I love linux, but it doesn't handle low memory situations well[1], and whatever Chrome does in low memory situations makes it much worse. Tab discipline is the most important thing you can do. I have an obscene amount of tabs open too so I feel you. I've started making liberal use of the Session Buddy extension and that is helpful, though my true fix was putting 128 GB of RAM in :-D

[1] This is improving greatly in the last year or two, but that probably wouldn't have made it to your chromebook.