This is happening and I apologize if it's not totally clear as I am going by memory this morning from last night.
Here is an example: (Don't remember exact channels in exact cues but it doesn't matter.)
Have 130+ cues.
During tech Sunday I discovered I did not have Auto Mark on so I turned it on and everything marked as expected.
Last night second tech when I ran cues 71 and 72 I discovered nothing changed from cue 70. The screen showed cues 71 and 72 as blocked (b) and the first column for timing is blank in those two cues. So cue 70 remained the visible cue through cue 71 and cue 72. (These are all conventional channels in these cues)
Later in the tech last night I added a channel to a different cue using update cue enter and discovered the next cue after the changed cue, which had that same channel in it already, was also blocked (b) and the timing column was blank.
When I did Undo the last update cue the previous cue of course no longer had that added channel in it and the next cue went back to normal with the timing showing in the first column and no (b).
Scratching my head here. :-) Is it expected that when a channel is added to a cue that already has that channel in it in the following cue that channel will auto block in the following cue and prevent the cue from running?
I have no idea why those two other cues became blocked unless I added a channel in cue 70 that existed in cues 71 and 72 and I don't remember doing it.
Still doesn't make sense.