The number of frames will match the length of the sequence asset not the custom range specified in the BP.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-152627 in the post.
|Component||UE - Anim - Sequencer - MRQ|
|Created||May 16, 2022|
|Resolved||May 17, 2022|
|Updated||May 19, 2022|