setting parameter "_db_flash_cache_max_slow_io" and "_db_flash_cache_max_latency"

Oracle Database 18.3.2 Enterprise Edition on Solaris SPARC

with 2 Terabyte NVME disks setup as SMART FLASH CACHE

we have set the Oracle recommended values for these parameters

alter system set "_db_flash_cache_max_slow_io"=10000 scope=both;

alter system set "_db_flash_cache_max_latency"=200 scope=both;

but is still occasionally getting the SMART FLASH CACHE disabled

are the any upper limits for these parameters ?

what values are too high for these parameters ?

NB: we benefit a lot from FLASH CACHE, but the database hangs, when the FLASH CACHE is disabled.