If you manually upload the FIT file (without any modification) from your Wahoo to Strava, rather than the auto-sync, does it still give you the weird 4 second data?
Does it occur with every Wahoo indoor ride you do, or just some of them?
Certainly seems weird. I'd contact Wahoo support and let them know what is occurring, and your responses from Strava so far. Wahoo support is usually top notch and they might have had reports of this before and be able to point you in the right direction.