Well I think I have a bit nearer to the problem.
It seems to associated with Realdrums.

Here are some permutations.

C. / C.d = Stops after first bar/ Locks up

C. / C.b / C.db = Plays normally

C. / C.d / C.db = Plays normally

I have tried various combinations (too many to list here) and it all points to the insertion of a period after the chord name.
I thought it might be Realdrums, so I changed the track to midi drums and the same lockup happened
But if I define an instrument immediately after the drums bar, it plays normally.

Totally stumped !!!

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