Yes, if they are off line, it will delete them from global.
Can you give me a screen shot of that entire context window on the right hand side of node red? Refresh flow. I’d like to see everything that will fit in a screenshot.
The current function expects last_seen to be set to “epoch”, you have it set to “ISO8601”. Either the function node needs to be updated or the setting in Z2M changed:
Having the ISO8601 string in there is definitely more human-friendly, so maybe it could be worth making changes to the function node…