Stats not updating when using UDP under Mono

#### Issue details
Mission Planner does not show stats updates when connected via UDP. Setup is as follows:

F405-Wing -> Raspberry Pi Zero serial running MavProxy -> UDP to Linux machine running MP.

Connectivity works fine, and MP can download the parameters. During the initial connection, and parameter download, the HUD and stats update as expected. Upon completion of the parameter download, all stats (including HUD, stats on "Quick" tab, all stats on "Status" tab) no longer update.
A disconnect & reconnect repeat the behavior.

QGroundcontrol does not exhibit this issue.

#### Version
MP 1.3.70, Build 1.3.7431.6390
Arduplane stable 4.0.5
Mono 6.8.0.105
MavProxy 1.8.19

#### Platform
[ ] All
[ ] AntennaTracker
[ ] Copter
[X] Plane
[ ] Rover
[ ] Sub

#### Airframe type
Generic plane.

#### Hardware type
F405-Wing

#### Logs
I've attached a Tlog. Please let me know if there's anything else you need.
[tlog.zip](https://github.com/ArduPilot/MissionPlanner/files/4591666/tlog.zip)

Start by reproducing the Mission Planner UDP connection on Mono using the F405-Wing, Raspberry Pi, and MavProxy setup described, then inspect the attached tlog.zip around the parameter-download completion. Compare the update path before and after download; done means the HUD, Quick tab, and Status tab continue updating after reconnecting.

Written by the indexing model from the issue text.