Barking and whining in crate at night

We have a mini goldendoodle, just past 4 months old (18 weeks). He used to do really well in his crate at night. Would reasonably whine for a minute or 2 (I miss you), and then curl up for bed. Now he just sits and whines (sometimes little puppy yelps) for up to an hour! Like, what gives dog?! He goes out before bed, gets his water before bed, gets some cuddles before bed. All his needs should be met! Ignoring doesn't seem like the way to go, telling him "No" seems useless. Is this just a phase we gotta ride out? Any suggestions?!