I wanted to delete the factory-floor because I use editor extensions personal lab to quicly create bluerpints. But when I am done, I have a lot of different factory buildings that I cannot use, and therefore want to delete their floors to as they cannot be used outside personal lab. But when I deleted the factory-floor-1 I got this error:

The mod Factorissimo 2 - notnotmelon fork (1.1.20) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event factorissimo-2-notnotmelon::on_nth_tick(15)
LuaSurface API call when LuaSurface was invalid.
stack traceback:
[C]: in function 'index'
__factorissimo-2-notnotmelon/script/pollution.lua:8: in function 'update_pollution'
factorissimo-2-notnotmelon/script/pollution.lua:41: in function <factorissimo-2-notnotmelon/script/pollution.lua:37>

isn't 'factory-floor-1' the floor, where (by default) the content of all factories is placed on?

factory-floor-1 is the main surface used by the mod. Please do not delete this surface