Other Nullfs going "Stale" after a day of inactivity?

On FreeBSD 14, using nfs to mount pre-compiled versions of php over to different jails when theyre created with this here:
mountCmd := fmt.Sprintf("mount_nullfs -o ro /usr/local/php /usr/local/jails/containers/%s/mnt/", containerName)

so, this works fine. However, just come back to work from easter bank holidays, and ive noticed all the of mount points that have been created this way, have just gone stale. theres no sign of them here at all, im able to just re run a command to get it back, but its still bloody annoying.

So, does anybody know if im doing something wrong here, or if theres a better way to do this? would be much appriciated.
I meant to say nullfs, I dont really know if its the same thing or what the difference is to be honest this is the first time ive dealt with stuff like this