app_timer2.c from SDK v17.0.2 has a possible race condition in app_timer_start()
This calls the get_now() function which compares a "now" variable to a "m_stamp64" variable. The issue with this is that both of these are uint64_t types so are not atomic and m_stamp64 is modified from within an interrupt context so could get clobbered during the compare.
Instead this get_now() function should be deferred until the RTC interrupt context to ensure it's validity
EDIT:
Just noticed that this also applies to "m_base_counter" which is also modified from within an interrupt
