I updated the Bedrock Server to version 1.16.210.06 and now I am unable to connect when using my world from the previous version of 1.16.200. I've tried older backups with no luck. My Minecraft Client is updated to the latest version. Tested with PC and Mobile.

I understand how port forwarding, NATs, firewall, etc. works (I've had this same configuration for over a year on my server) so that is not the issue. I am able to connect to my server ONLY if using the default Bedrock Level that the server creates when it is first launched.

When I import my world to the server file it always says "Unable to connect". 

I've successfully updated the server for over a year with previous versions of Minecraft with no problem. This is the first time this has happened.

UPDATE:  ** I was able to get it to work by deleting the "level.dat" and  "level.dat_old" files from my worlds folder and started the server. The server then made new "level.dat" and "level.dat_old" files. I am now able to connect. Is this a known issue?