When my ubuntu18 system connected to mobile hotspot, it always appeared that “wireless network activation failed” and the password entry interface popped up repeatedly
A relatively simple solution is:
open the terminal and execute:

$ sudo pppoeconf

If you have an option, choose Yes
Then change the wife password to 10 or more digits, preferably all in combination
Then see if the connection works, and if that doesn’t solve the problem, find another solution
Done!