I got this behavior with "session":{"restore_on_startup":1} in ~/.config/chromium/{profile}/Preferences.
I only get this on my laptop, for some reason, not my desktop. I can set that to 0 instead of 1 and everything is OK, except my saved tabs of course which are not restored. Also, I've noticed that having that set to 1, I can sometimes close Chromium and open it again. I'm not quite sure on what the condition is, but closing it down with Ctrl+W, tab by tab down to the last one, seems to cause the issue, and closing all of Chromium with Ctrl+Q actually seems to work better. Again, not 100% sure about this. For some reason, opening with --disable-extensions works around the issue, too.