Inserting bars causes ghost notes

I have a large orchestral piece into which I need to paste 170 bars. the space is 70 bars. I deleted everything in those bars and tried ctrl insert 100 bars. That created a crash of sound on bar 1 and a continuous ghost single cello, or viola? note right through all 1000 bars of the whole piece.

I tried putting in just 50 bars same result.
20 bars down to 12 bars I get a Timpani beat when I start playback. Inserting 10 bars or single bars doesn't cause the ghost notes.

I can work round it, but it's time consuming having to only insert in tens of bars.