When using the + and - buttons to insert a new pattern into the matrix, for sufficiently complex tracks, it can take several seconds of a completely locked Renoise before anything happens.
The weird thing is that using the shortcut keys to do the same operations make them complete without any waiting time at all. Why would using the buttons to trigger the same action as the hotkeys cause such a massive slowdown and locking of the Renoise UI?
It is not the same to insert a new pattern in the sequence at the end as in the middle or at the beginning. In the latter case, Renoise rearranges the sequence, and that may take a while. This can be significant when there are many patterns. Maybe it’s related?
The button action and the key command action should be exactly the same (take the same).
Maybe you should contribute a song where this happens and name what operating system and version of Renoise you use. Maybe someone will find the problem.