Odd.
If it was just one video, I'd ask if you forget to end recording before shutting down.
Happens a lot to newer drone pilots, but an easy fix usually (you put the card back in, fire up the drone, and usually the last missing video will be saved to the card then).
But vids and pics missing in higher numbers makes this scenario less likely to be the problem.
You've been using the microSD card successfully before this ?
It's a good quality, high speed card as recommended by DJI , or higher specs ?
Oh, welcome to the forum too.
Pretty quiet here now the Spark is becoming less and less used by pilots, so obsolete now.
Still, many still love them, they are an exceptionally good little drone for their time, and a lot of fun to fly still.