I've experienced the same issue in 1.15.2 and was able reproduce it in 20w19a.
Reproducing it is a bit tricky, as you have to place the fence right in the moment when a chicken walks on the block where it should be placed.
What worked best for me was building a small space (e.g. a 3x3 area enclosed by fences), then placing a few chickens in it and then trying to place a fence in a corner block surrounded by chickens.
Sandor Herms
I've experienced the same issue in 1.15.2 and was able reproduce it in 20w19a.
Reproducing it is a bit tricky, as you have to place the fence right in the moment when a chicken walks on the block where it should be placed.
What worked best for me was building a small space (e.g. a 3x3 area enclosed by fences), then placing a few chickens in it and then trying to place a fence in a corner block surrounded by chickens.