When the research for "Factory Input Belt Unlock Extreme Fast Belt" is done the game crashes with the following error:

The mod Factorissimo2 Playthrough compatfix-notnotmelon (1.2.4) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event Factorissimo2-Playthrough-notnotmelon-compatfix::on_research_finished (ID 18)
...imo2-Playthrough-notnotmelon-compatfix__/scripts/gui.lua:313: attempt to index field '?' (a nil value)
stack traceback:
...imo2-Playthrough-notnotmelon-compatfix__/scripts/gui.lua:313: in function 'handler'
core/lualib/event_handler.lua:47: in function <core/lualib/event_handler.lua:45>

Fixed it in code. If someone is interested the code for Factosrissimo2 Playthrough(F2P) stores the belts as 'name-' and appends 'transport-belt' for operation. The problem is that Ultimate Belts(UB) uses 'name-' + 'belt' and so F2P create for example 'ultra-fast-transport-belt' which doesn't exist because UB uses 'ultra-fast-belt'.

Fixed in latest