Apparently the internal RAM needs a clock to be above 12 MHz to avoid data loss. According to section 5.3.1 of the user manual, the main clock needs to be > 12 MHz, according to section 2.1, the CPU clock needs to be >= 12 MHz. Which one is it? Depending on the value of GCSR, they might differ (e.g. with the default value, the CPU clock is one eighth of the main clock).
Spth, I would suggest you submit a support case by going to my.digi.com and logging in.
I see two references (2.1 and 36.2.3) indicating a minimum of 12MHz, so let’s say >=. Because of clocks not being 100% precise, I’m guessing it will even work at 11.999999MHz.
Digi no longer sells the chips, and the Digi products using them (which run at speeds well above 12MHz) went EOL in January 2025.