Same Issues as OP. Message started acting up when I recently flew and put my phone on airplane mode, and selected the airlines new onboard wifi.
Problem Manifestation: 1) Selecting Messages either presented a black screen, or 2) Messages screen frozen 3) sending a message failed with a blue line in the Message screen showing the message was being sent, but would take 10+ minutes then fail, 4) Incoming messages would show up delayed (if at all) by 20-30 minutes and only show in the banner, but not in Message. I would have to do a hard reset (sound up, down, the press and hold the right side button. The message would appear once rebooted, 5) Going into settings and clicking either Messages or FaceTime would hang iOS in Settings. Swiping the Settings screen close would return iPhone to the prior state.
Attempted Resolutions: 1) Hard reset, 2) Turning Message off in Settings (after doing a few hard resets) 3) Repeated with FaceTime. 4) Hard reset and turning Message back on. 5) Cleared space on iPhone storage 60 GB available) 6) Used on Cell service, switched to WiFi – no success.
Recent Changes on iPhone: 1) Added an eSIM 1 week ago for travel to Japan., but iPhone was working fine for a week. iOS is set to automatic.
WHAT WORKED: as another poster said, turning off FOCUS in Messages )Settings) seemed to work.