Spalts can be a challenge to pop mainly due to the extreme porosity of the timber.
In my experience, there is already enough going on with spalts and popping can be be detrimental.
Usually you will find a lot more figure will come out when you apply the finish.

IMHO, the best course of action is to make a slurry (consistancy of thickened cream) of timbermate and use a rubber squeegee to force it into the pores before sanding..
Let it dry overnight. Timbermate does need some time to harden, it may feel and look dry but it still needs some time to cure.
Then give it a light sand with 320 grit to flatten out the surface.
Check it to see if there are any spots you missed and apply a second coat of timbermate if needs be.
Then sand the top carefully with 320, remember spalts dont require a lot of sanding.....