A recent change to the RSA key generation process is capping the number of attempts of finding a probable prime to a multiple of the prime's size, in FIPS builds. This means it might fail once in a while. (It could also fail for a couple other reasons but this is the most likely.) The API is changed to retry key generation until it succeeds. Non-FIPS builds keep trying until they find a prime.
Before creating any new configure files (.conf) read the CONF_FILES_README.md