I dont know if its a bug or more likely my computer but im making a competition level which has a lot of customised terrain (no custom styles just existing styles edited with erase function) and Im finding the editor to be super super laggy it keeps freezing and i have to wait at least 5 minutes.
Very likely to be your PC. While erase vs normal shouldn't make too much difference (No Overwrite is the one that will tend to cause lag), having a lot of pieces in general means the editor needs to do more work to render the level. This isn't so bad in NL itself because NL only renders the level's terrain
once, then keeps the result. The editor can't do this because individual terrain pieces can be moved, as a whole, at any time (vs in game where, while
pixels of the overall level's image can be modified, there's no need to care about individual pieces anymore once gameplay starts).
This in turn means that, on a weaker PC, it will take longer to render. Now it may be possible to improve the rendering speed somehow, but, this isn't a priority.
On my PC, if I open LPV Outrageous 15 "To Infinity, Beyond and Back!" in the editor - my largest level at 976x480, and
probably the most pieces (though I haven't actually done a count for every level, just guessed) at 1568 terrains + 58 objects, I see very, very slight signs of lag - not to the point it would even be slightly frustrating to work with, but I
can notice it's there. My PC is a high-end-for-its-time but slightly old now (2016 model) laptop. I will note that 1568 is
extremely high for the number of terrain pieces - by comparison, two other levels i have that are somewhat comparable in terms of size, "Goodbye Galaxy" from LPIV and "The Lem Goldberg Contraption" from LPO2, both have under 600 pieces each. On these two levels I notice no lag at all.