Dropped Frames FS7 / A7s iii Timeline

Hello,

Been trying out the caption feature and I a bad hitch or about 30+ dropped frames every time a new caption is loaded on the timeline. Happens when trying to play captions over a7s III footage. 

It is 4K multi-cam footage with two cameras, one fs7 and one A7sIII, and a look applied, but my computer has no problem playing it back. Once the caption layer is applied it has a bad hitch every time the caption changes to the next caption. 

The hitch doesn't happen with the underlying FS7 footage, but constantly happens with the A7s III footage layer when that is the selected camera. 

File properties for a7s iii: 

Image Size: 3840 x 2160
Frame Rate: 23.976
Source Audio Format: 48000 Hz - 16-bit - Stereo
Project Audio Format: 48000 Hz - 32 bit floating point - Stereo
Total Duration: 00:29:03:12
Pixel Aspect Ratio: 1.0
Alpha: None
Color Space: Rec. 709
Color Space Override: Off
Input LUT: None
Video Codec Type: MP4/MOV H.264 10 bit 4:2:2

My computer has plenty of overhead and I'm reading the footage from 5 GBPs SSD so the disk is not the bottlekneck here.