I've made a general comment for your "omg it's broken, switch to something else immediately". The rest was specific to WiFi Inspector, how it works and why in your SPECIFIC example with your ISP it somehow became a problem.
Just as you have the right to post it and notify others about the issue, so do I with explanation why exactly it happened and how to remedy it. What else do you expect at this point? Magic wand that forces your ISP to magically change their software infrastructure? C'mon dude, be serious. There is no mass user disconnection going on because of avast!. Your case is a very specific scenario. And I'm not deeply emotional about avast!, I'm deeply emotional about people experiencing dumb s**t and then blaming it on the wrong party, be it avast! or someone else (if you haven't noticed I blamed ISP as well, which includes my own as well because they use stupid account control panel as well and it's dumb as hell, mine just doesn't disconnect me for probes). You should see me go ballistic when people blamed Microsoft for BSOD's in Vista and 99% of BSOD's I've later inspected were caused by a system driver starting with "nv". Which was NVIDIA. But people blamed Microsoft because "muh Windows showed BSOD and I didn't like it". And I was using ATI back then. So, clearly, I wasn't defending Microsoft because I was "deeply emotional" about Windows Vista, but because it was a common sense for me to point out what actually caused the problem and not just blindly blame someone. It helps users who read such things in the future. If your solution is to switch product, then you're not really telling anyone why all this really happened and what exactly caused it.
Can you tell me what your ISP is at least, I'll ask avast! devs about something if it's possible to make blacklist of ISP's who terminate users for using WiFi Inspector based on IP owned by user. So that WiFi Inspector would simply return "Not allowed to run on this network" in case users have blacklisted ISP, preventing unwanted disconnects due to WiFi Inspector probing. That's about most avast! can theoretically do about it really.