Thank you everyone for the responses!!!
I prepared another jar of varnish, and added only a minimal amount of turp and then thinned with spike lavender oil, and it seemed to have solved the problem. I tried it on another instrument and it seem to be fine so far. I suppose I must have put too much turp already when cooking the varnish, maybe. The varnish is the only variable I changed this time from the previous five times.
I only scrape (off the specks of dust etc) between layers and never tried sanding it.
As for silicone, I don’t think I have anything silicon based in my shop, but if it’s in so many products I will make sure to check everything I bring into my shop just in case it contains silicone.
Thank you, thank you everyone. I hope this doesn’t happen again, fingers crossed.