Anyone else’s babies suddenly crying at naptime and bedtime?

This started yesterday. My son has been putting himself to sleep for quite a while now but yesterday each time we put him down for his naps and for bed, he started crying inconsolably. He would just stand up in his crib and cry and cry. It happened again today for his two naps. Yesterday, I ended up going in and rubbing his back until he fell asleep and did the same for his first nap today. But for his second nap today, I ended up letting him cry it out. Is that horrible? I don’t know what’s better to do. I don’t want to start any habits such as me going in every time he cries but I also hate to hear him cry. He is a little over 10 months old and he is currently in Leap 7 so could this be because of the leap? Should I just let him cry it out? Please offer any advice...thank you!