Could be FS-UAE issue, never happened to me. SDL and CGX versions have different input code so it may not occur on both of them.
Viewing post in VanillaConquer - Amiga port comments
I confirm, the issue happens on both WinUAE v3.3, v4.2 and v5.3 and FS-UAE v3.2.11.
The problem happens with:
Vanilla Conquer (non vampire) r1.2
Vanilla Conquer v1.0
Vanilla Conquer Tiberian Dawn r1.3
No problems running with:
Vanilla Conquer Tiberian Dawn CGX r1.3
Im using an A4000
ROM: Kick40068
FPU: CPU internal
CPU: 68040
2MB Chip
512MB Z3 Fast
JIT enabled
RTG: Picasso IV Zorro III
using directory Hard-Drives
I also tried switching around some options
Unless you have any suggestions, I will probably end up using Vanilla Conquer TD CGX version as it also has the video playing fine. My problem now is I cant find any link even after purchase for vanillatd.7z or VanillaConquerTD.zip available for download anywhere right now.