If you’re a nursery nurse, then you’ll know kids can be little shits for absolutely no reason ;-)
In all seriousness though, kids having a preference for one parent is fairly common, often a phase, and (although easier said than done) shouldn’t be taken too personally. Even if it’s a painfully long phase. Just keep showing up for your DC in low-pressure situations and things are likely to turn around eventually.
My DM also works with children and is amazing with them. She was a SAHM when I was little, and then worked very part time when I was older. My DF worked long hours and travelled frequently. So of course, I adored my DF and made my disdain for my DM extremely clear (huh???).
I’m deeply ashamed of this in hindsight, but literally from birth (I’m told) I didn’t want her to hold me, to touch me - ANYONE was fine but her. I honestly thought she was cringeworthy and pathetic. I assure you, she is neither of those things!
I’m now 30 and she’s one of the first people I call when anything is on my mind. We’ve had a strong relationship for a decade, and especially since I had my DCs. I genuinely enjoy her company. (I still like my DF too!)
I have no idea what changed. But when I’ve mentioned this guilt over how I used to feel about my DM to therapists in the past, they have told me it’s a pretty common feeling and not to read too much into it. I hope that this is a (frustrating) “little nothing” for you too. And I hope that it changes soon! But try not to feel too rubbish about yourself or about the fact that you work in the meantime. You could be a SAHM like mine and still be in the same situation, but with less income and more risk!
On a side note, might be worth talking to your GP about your DS still being non verbal at nearly 3. Could be something to watch out for. Also, you might find that you have more in common with him once you start having conversations. My DD and I have always been close, but it’s really in the last year (age 5) that we’ve started having mounds of fun in each other’s company.