I tried to merge (advanced) CUE 1 from another show to CUE 2 in current show and when started merging the current show disappeared, I had to load the show, I tried 3 times same result.
V3.0.0 build 389
RPU Xe as Master, ION Xe as backup
Were you merging on the Backup from a File on the Master? If so, this may be a bug. The workaround is to merge from a file saved locally rather than on the networked console.
Yes, I was merging in the Backup from a file on Master,
In this case I believe this is the bug. My apologies. It is being tracked as EOS-51438. If you open the show on the Backup and save a local copy (or save to USB and move it to the Backup) then it will open without issue.