Playing on a 1.15.1 server hosted on my machine. I've noticed that certain blocks in my pumpkin farm will never be affected by random tick updates.
In the image I'm standing over the problem area. I bonemealed all the plants to maturity except the one to the left of my hotbar, which still hasn't matured after many hours of gameplay nearby it. The grass never spreads to the dirt next to it, and all the pumpkins that are missing never grow. There's a chunk border between the plants and the pumpkin's targets, but going down the line they can grow before the chunk ends. Everything else around the area works fine so it's definitely not either chunk glitching.
Despite watching many technical things from people like ilmango (yt) and having a decent understanding of Minecraft's mechanics, I have absolutely no idea why the game might be doing this.