As far as why you now get more channels, when the analog channels were finally turned off, many digital transmitters were allowed to increase their output.

Plus, many of the digital channels were allowed to move to a different, and more desirable, digital frequency so that is why you probably got more channels after rescanning.

As far as why your channel cuts in and out, it is likely atmospheric conditions affecting a marginal signal. Perhaps re-aiming your antenna would help.

jdbillp is correct about the atmospheric conditions causing some signal loss. A good way to minimize this on a channel you may want to be taping would be to look at the signal strength on the channel you want to tape. Adjust the antenna for the strongest possible signal.

In the summer months as the day moves on, the atmosphere between your antenna and the transmitter can become thicker with pollen, smog, dust, etc. A marginal signal will then be impeded. In the evening when a lot of the particles begin to clear such as condensing with the evening dew, the signal becomes clear again. You can evidence this by scanning late evening and early morning.

Also, as jdbillp mentioned, some of the stations you never received before now have a stronger signal. Some of the analog stations you may have received clearly are now coming in with a weaker signal. Some stations have been applying for, and receiving, permission to increase their signal strength. I think once this whole conversion process is a year old, you'll find it will become a bit more stabilized and consistent.