I rebooted the instance, started the docker container and metrics are back. It may be that the instance was too small for 3 RDS servers (two were very small) I removed all but the most important and purged the other data. I did this for BOTH mysql:metrics and mysql:queries. However the queries still show up for the 2 dbs I removed. Now the prometheus/targets are showing up for the one db I want & down for the other two. (not sure how to remove them?)
Turns out the old PC standard worked. REBOOT, restart.