Log1-Why user thread not run after use latest system-firmware?

If your device stop working after update to latest system-frimware,Please read this post first before set one issue to particle github.
1.Try to use the latest firmware
2.Device not work!!!
3.Write a user software do nothing but printf message "I am alive"
4.No output
5.Some API block again???
6.set one issue,m-mcgowan ask me to update bootloader
7.After update bootloader,It works
If your cloud do not support update bootloader you should be very careful.
Thanks m-mcgowan!He is very nice!

Thank you for your helpful instructions!