Yup, even when "not overclocking" clock speeds are set and vary. I'm also a (very recent X) R5E user, I regularly used to get boot issues, usually CPU over voltage, or overclocking failed errors, followed by a regular ritual bios self destruction! that said once it was "up" it was rock solid, even at 2.5 ghz on all cores.
As above I'd recommend choosing XMP, setting the correct RAM speed, check the recommend RAM voltage for your RAM try the latest bios if you are not already.
Are you on the latest intel chipset drivers and firmware?
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