It is normal, it doesn’t necessarily mean they have sided with your husband, it might just mean they do not longer know how to behave around you now that you are “single” especially if many of those friendships were about spending time together as couples, they may simply try to avoid hurting you by playing “happy families/life is normal around here” in front of you.
One thing you may need to understand is how “mutual” those friends are, if they were the friends of your ex when you met them, they are still his friends, much as those you introduced your ex to are yours…Unless you or he have done something very very significative (good or bad) to make people change sides.
This may be healthy in the long run, it avoids all that hurtful gossip going in both directions. Most of our mutual friends were actually mine, they only had contact with exH through me (like going out as couples) so contact with him stopped altogether as soon as he was not coming with me.
The ones who stayed in touch with both of us turned out to become a nightmare, someway they couldn’t understand that talking to him about me or about him to me during the nastiest parts of the divorce process was not only thoughtless but blooming costly: For example, my neighbour’s son got a new car and started parking it in front of my house, well intentioned other neighbour told him I was happy without him and had found someone else who was often at my house… so we spent an extra year in court (add another £10,000 in solicitor fees) with exH often sitting outside of my house in his car in the early hours and him trying to prove I was cohabiting with someone else so he could get a higher percentage of the assets.
Similarly, I didn’t enjoy friends coming to tell me how happy or unhappy he was, I didn’t care really and at some point I decided to cut contact with all the “real mutuals” as they couldn’t understand how the blooming gossip/just trying to help was making things far more difficult for my ex and I but also for our child.