Hey Oliver,
Ok this is something I have had in the past and really needed to work in as well! Just doing lots of irregular drills is the best way to fix this problem. One of the best is just getting someone to block you anywhere in the table and you have to topspin into their backhand, this helps yoh start to read where the ball is going better and not guess to early.
Also Multi-ball is a great way to speed up your movement and become more stable because it’s faster than normal speed play so you get used to switching and anticipation of shots and in games it becomes easier. The last thing is just to try as much as you can to stay relaxed and loose in games, if you are tense or stiff these moments get a lot harder and you will feel rooted to the spot. Let us know how it goes!
Dan 🙂