Transmitter reboots while switching model with "s.bus trainer" to model with MULTI or s.bus external module (X9D+)

[prikrylm]

Describe the bug
Transmitter reboots while switching model with "s.bus trainer" to model with MULTI or s.bus external module (X9D+). Only direct switching produce restart. When as first step I switch to model which has internal module as transmitting device, and then switch to the model with external module, no reset occurred.
Problem occurred only on hardware radio, Companion's simulator works well.

To Reproduce
Steps to reproduce the behavior:

1. Set s.bus trainer on model
2. Switch to another model with external module as transmitting device (s.bus external model alternatively)
3. After while transmitter restarts and model with s.bus trainer is selected.

Expected behavior
Transmitter switch to selected model.

General information

• OpenTX version 2.3.10 (stable)
• Hardware Frsky X9D+ (pre 2019)