Premiere pro 2024 lags when exported although it’s perfect in the timeline

hi, could someone please help me out. I have been trying to figure out this problem for hours and I have got nowhere. When I export my video the quality is great, runs smooth etc, but there is 3 clips that just lag and this is only when the video is exported. I would appreciate some help as I need to get this project sent over asap. 

many thanks