No, this is normal that it drops a little (maybe 0.2-0.4 over a couple minutes). The pumps automatically turn on every 2 minutes from what I've counted. I've had the problem in the past where it was running for what seemed like every 30 seconds. If it's going under 18.5 it would run prematurely and that would indicate a problem with the pressure, but this doesn't seem to be your case.As far as the meniscus vacuum, it always seems to be around 18.8-19 units so there must be some sort of leak.
One time my purge pressure was 4,7 and printer was beeping —problem was caused by slightly lose connection between air pressure tubing and circuit board sensor that measures air pressure.
Not sure what other advice I can giving other than going through entire line and checking for any lose connections.