The December 16th updates (1.19.3/2 and 1.20.1 for sure) are broken.

[KyraArden29]

String lights won't place on blocks (will on fences), they only leave behind a connector. Strings also aren't stacking when they're the exact same type/bulb order. Bulbs on servers aren't showing up properly, ie. one player places a spider and the other sees a generic bulb. These are from the comments as well as my own experience. Hope this gets fixed soon.

[stinkymayo]

Having this exact same issue. I didn't realize they even worked using fences. Really hoping this gets fixed soon :(

[stinkymayo]

I have also discovered you can not craft the hanging lights with using a stick instead of string.

[vinnyg0621]

having the same exact issue here. i really hope it gets fixed soon