All normal-pri user threads suspended for two seconds shortly after WiFi connect starts?

Firmware
4

I do not have experience using threads. However, I have checked out some documents, on this forum, you might find useful to solve the issues you are encountering. I will list them below.

System resources are not thread-safe. The USB serial debug port (Serial) can only be called safely from multiple threads if you surround all accesses with WITH_LOCK(). An example would be changing the following line

 Serial.printlnf("-- Current state: %s", g_State->getName());

to

WITH_LOCK(Serial) {
 Serial.printlnf("-- Current state: %s", g_State->getName());
}

You might find these helpful:
https://community.particle.io/t/particle-threads-tutorial/41362

https://community.particle.io/t/delays-in-multithreading/50338