AIO for refusing to visit my sister at her house because her husband ignores me

Over the past two years, I (26F) have visited my sister’s (34F) house where she lives with my niece and my brother-in-law (38M) at least once a week. My BIL is rarely around when I visit, since he works long hours and usually gets home after 8 p.m., while my sister works from home part-time - I visit on her days off.

When I’m there, I help out with my niece, clean up after dinner, and babysit while my sister runs errands. I don’t expect praise for helping, but I find it odd that whenever I’m over, my BIL is never the first to say hello. There have been times when I’ve been feeding my niece and he’s walked right past me without even acknowledging me. I never mentioned this to my sister, but a couple of weeks ago she saw him leave the house without acknowledging me yet again.

I told my mother about it, and she said he might be on the spectrum and that I should excuse his social missteps. But my BIL works in a high-paying, people-facing profession with a lot of responsibility, so I struggle to understand how he can be perfectly social at work yet unable to greet me in his own home. It’s started to make me feel uncomfortable and a bit disrespected, and I’m wondering if I’m overreacting or if this is something I should address with my sister.