Dear Khun Pranee
TIV has the same issue as you mentioned, We can not 100% resolve this issue but can reduce by following points:
install air to blow the needle , to cool down the needle during penetration.
the adjustment of rotary hook and sewing needle should be slightly touching only i.e. no pushing
try to use needle Groz Beckert GEBEDUR R/70 (gold needle), SCHMETZ SF/70, or Groz-Beckert SAN 10 XS 70,
Please do first the above steps before you do the below last step. If the above steps can resolve your issue, its not necessary to go to the below step because it's needs closely monitoring.
slightly wet the filter by silicon and put on the top of thread stand, put dry filter above the needle bar where the sewing thread can pass through to dry before stitching into the garment to ensure no oil stain issue appear after sewing. Hereunder the photo for your easy understanding
Furthermore, we also raise TT to TPDM for the time spending on cleaning the white dots and their advise on how to solve the issue.
We are hoping, the above mentioned steps can help you to solve the issue.