After my debugging and findings as of 20201019, the procedure to replicate has been updated and I can reproduce this 100%/Always.
# Make sure your PTT button in Arma 3 is bound to a key (eg CapsLock). "Settings -> Controls -> Multiplayer -> Push To Talk -> Bind it to a key".
# Enter EDEN editor via Altis Map.
# Place down a 'game logic' and paste in the following code...
0 enableChannel [false,false];
1 enableChannel [true,false];
2 enableChannel [false,false];
3 enableChannel [false,false];
4 enableChannel [false,false];
5 enableChannel [false,false];
6 enableChannel [false,false];
# Place down a playable unit and enable unit as 'playable' for multiplayer (double click unit, Object: Control, Playable = tick).
# Top Menu, Play -> Play in Multiplayer (MP)
# Once loaded in, if VON is not locked ON already, press your PTT button at least once, then press your < and/or > key to cycle channels.
# Continue to press your < and > keys to cycle VON/TEXT channels (Side,Group,Direct,etc).
# Note that VON is stuck on, and pressing the PTT button makes no difference to turn it off.