So.. When I talk about my gender, my family and friends are universally supportive... They suggest their own gender neutral terms, they ask my pronouns, they really seem like great allies. And then, as soon as I stop talking about it and things go back to normal, it's like I never said anything. I'm "she" "sister" "girl" again. Everything I worked so hard to figure out about myself, that I felt brave for sharing... It all meant jack shit to them. No one cared. And how do I even deal with that? They're not against me. If I say anything, they'll be "for" me again. But if I'm not raising a fuss (because I only have limited energy for fussing, and ultimately would like for there to not be any fuss) it stops mattering. I disappear again. I can't force people to care, so what do I even do...?
Correct the probouns without fussing? Also give them time to adjust. Use your preferred pronouns with them regardless.
It might simply be the force of habit. About 20 years of calling you like this stays in the mind as a reflex. I remember being so angry with myself when I used she/her pronouns when talking about my ex-love/now-bff for a while after he became who he is, it was very frustrating for me, fortunately he brushed it off with a laugh. But yeah, my bet is on the habit. Don't you have this old relative who called you by your mother / aunt / older cousin's name for years? Hang in there, and point it out to them kindly when it happens. It will soon get adjusted in their mind, strongly enough to cover up the past automatism.