Hold the planks in your hands. Make sure you have enough. I think you need a whole stack of 10. Maybe 8. To combine them, put one in your hands and hover over the item you want to combine in the vicinity area and it should let you push O to combine.

Try exiting server and reloading always.

For real they need to fix this. It happens in open fields and everything once you hit fourth gear. Or you are near trees or buildings. The game lags and freezes and loads back up after 10 seconds or so. Sometimes it causes the player to have to reset the application on console. Very frustrating to have this happen and then get blasted on. Do players near by mess with my connectivity? Wtf???