Caused by 18b693bdbd6b, due to lack of thread safety.
Beteween calling BKE_sequencer_cache_get_num_items and BKE_sequencer_cache_iterate
New items could be inserted in the cache.
BKE_sequencer_cache_iterate() now use 2 callbcack functions for initial setup
during which buffers with correct length can be initialized and finally iterating.
Additionally drawing of unselected items was fixed again introduced in 18b693bdbd6b.
T74662 is reporting quite different symptoms, than I get on my machine, so I am not
entirely sure this is complete fix.