Hello @werovsee ,
Thanks for your post.
Are you using a reference board or a custom board?
If it's a reference board, what is the SCH Version of the board (there is a label pasted on the back of the board)? And please refer to the FRDM-K64F Board Errata to check if it matches the situation.
If it's a custom board, you can refer to the errata for MK64FN1M0VLL12 and see if the following workaround is effective.

BRs,
Celeste
-----------------------------------------------------------------------------------------------------------------------
Note: If this post answers your question, please click the "ACCEPT AS SOLUTION" button. Thank you!
-----------------------------------------------------------------------------------------------------------------------