So, I decided to transition to the Google Play version of signal and I still had the problem of flaky notifications and missed calls. I think I have narrowed down the issue. I have two profiles. When I am logged into both profiles, Signal (in the main profile) works flaky as described. When I restart, signal works perfectly until I re-login into the second profile.
It seems that other notifications from apps in the main profile are also delayed when logged into both profiles.