I know some things loose visibility if they fall out of the margin, usually happens on refrenced parts, didn't know it could happen with a pattern.
Save the assembly as a copy, and remove all but the pattern.
post the assembly, part, and drawing, we can figure it from there.
Hmmm... The pattern has a visibility seperate from each element, and parts have their own.
did yo check all three? well two anyway. as we know the root pattern object is visible.
If the assembly is too big to make a copy or if you think the size of the project may be the culprit, demote the pattern temporarally and try it by itself in its own assembly.
Wait, one last thing to try. Make that view shaded just to see if the part will show.
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