This was a thing many years back where FlyingBlue was known for doing this with new accounts that were hit with large transfers of CC points into the program to book flights. It was an anti fraud based action. In these actions some people were able to get their miles and even sometimes tickets back after verifying their identity and going through some steps. Others may not have.

Are you seeing recent reports of this? or old ones?

I've created accounts for family members and transferred in their miles to then have them log in, so different IPs, to book without issue several times the past 2 years so I'd say the risk is far less than it used to be.

You can also go about making accounts at the most popular C1 transfer partners to have them established for future use.