I saw this folic acid tt link a lot on mn last year and was confused as I thought that tt was actually linked more to 'midline defects' which is why we take folic acid. (Spina bifida etc)
Tt can be genetic and is linked on the fathers side - my son had a posterior tie which left his tongue a little restrained and a high palate (caused by lack of movement by the tongue) which makes it harder maintain a latch. I can clearly see my Dh has exactly the same tongue and it has a slight v when he sticks it out. My son's was cut at around 11/ 12 weeks too MrsJ.
This article explains the other possible cause of tt, with folic acid but it's not caused by folic acid (article explains it better!) I do know midline defects have been identified as common in families who have this gene and successfully treated with folate.
Also, I imagine the tongue structure develops during the first trimester, when we are all taking folic acid.
There's no issue continuing to take it; my mw explained that many prenatal vitamins are v expensive so they let women know when they can stop buying them. In reality, with a broad ranging healthy diet, eating the foods recommended by the nhs, you only need folic acid and vit d, and then only vitamin d (cos we're sun starved!)
I took pregnacare throughout my first pregnancy and most of this though I've been less consistent!
ruminanaturals.ca/2016/07/01/tongue-tie-is-folic-acid-to-blame/