Nighttime Separation anxiety?

My 7 mo was ferberized at 4 months and has gone to sleep independently for bedtime and naps since. Currently on a 3/3.25/4 schedule. Naps capped at 2-2.25 hours total. However the last two nights, bedtime has been uncharacteristically awful. Immediate freak out when I walk away. Tried Ferber check ins and resulted to CIO last night. I kept him awake 15 min longer today, but it Happened again tonight and his crying was off the walls upset. So I’m currently rocking him to sleep. My best guess is separation anxiety? He went to sleep independently with his naps today tho? Anyone else experience this? I don’t believe it’s under tired but I could be wrong?