Google AdWords says they check on regular bases. One also said to wait couple of weeks to be sure. If you don't see a change in your QS and you are certain they should happen, try phoning them and asking for check. Person you will talk to cannot really help you but will politely tell you she/he will pass it onto the team and that they would get back to you.
Please be aware that changes required by Google AdWords in order to make QS better are enormously big, in other words, almost new site. I havenít heard (or experienced) that alterations here and there ever affected QS.
FWIW, my logs show that lately the AdsBot has been visiting the destination URL of an active ad every 14 days.
If you are able to copy the page to a new URL and create a new ad variation with that new URL, that can help prompt a visit from AdsBot. But the main drawback of doing that is that the new ad won't have the same quality score history as your current ad. It's worth trying, though...better than waiting up to 2 weeks. If it doesn't do anything useful, just pause the new ad that you created.
Looks like G is messing with our heads again. Basically, it won't send the Adsbot after the initial check in order to make it so people can't make the changes quickly. Basically, another little thing to make our lives hell. It will only re-send the Adsbot when it feels like it. So according to "do no evil", noone is capable to fix their landing page quickly, it must be a long process of at least a week or two. And if you fixed it quickly, that's not good enough - you should work on it for at least two weeks. What kind of BS is this?