Premiere Pro 2023 Waveform comes out as block

I have never seen this before.

My waveform looks fine but suddenly near the end of my timeline the waveform has turned into a large block!

it is a nested sequence of a video podcast.

I have done 90min to 120 min video podcast editing before but this is the first time this has happened to me.

I have already erased my Peak files folder after reading about problems in another thread.

But It did not resolve the issue.

I'm on a M1 MAX with 32gig ram