Yesterday, October 18, 2019, was the day for Chicago TV stations to change their tuning parameters. Most of my Over-the-Air channels stopped working, until I rescanned.
Different towns will have different Rescan Day. You can find
info at TVAnswers.orgAfter rescan, most channels will be ready to go. There may be a few channels that will not behave as nicely as expected, for an unknown reason. For such channels, MC creates a new channel, instead of modifying existing channels (with correct physical channel number). So you might have duplicates, new and old. The old ones will not work.
Depending on your EPG setup and recording rules, you can decide whether to delete the old channels or manually modify the old channels and delete the new ones. The new channels, after rescanning, are placed at the bottom of the channel list. You can move them to where you like them before you decide which set to delete
My recommendation is to keep your old channels if you have many recordings rules that are tied to a particular channel. To do this, you should find the new channels and examine their parameters and see which parameters are changed. Edit the existing channel, and then delete the new one. This way you do not need to reschedule your recordings, nor do you need to take care of XMLTV ID mapping. As far as I can tell, only the "physical channel number" has been changed. So editing a channel is not too difficult.
On the other hand, if you do not have many recordings rules that are tied to a particular channel you can manually delete the old channel. If you have to delete the old channels, the new channels will not be associated with correct XMLTV IDs (if you use online EPG data). You will need to set them up by either manually entering the XMLTV IDs (having the old channels next to the new channels will help), or by running EPG scan manually and making sure you perform "match" operation.
To avoid having to delete old channels, it probably will help if you restart MC and do not play any channels before you try rescanning.
