The limit is 32GB. GRR means can’t access SDcard. Don’t understand why you would be getting AP mode unless you disconnected or your router is offline.
The SDcard holder in units before V6.4 were of the push/pull variety where you need to physically pull the card out as opposed to push/push where you can push the mounted card and it spring ejects. It is common for folks to snap an SDcard trying to pull them out with a fingernail. I usually gently pull straight out with needle nosed pliers.