Tried using this mod without Space Age enabled and got this error:

Error while running event BuilderBotStart::on_cutscene_cancelled (ID 179)
Unknown equipment name: fusion-reactor-equipment
stack traceback:
[C]: in function 'put'
BuilderBotStart/control.lua:192: in function 'EquipArmor'
BuilderBotStart/control.lua:240: in function <BuilderBotStart/control.lua:239>
stack traceback:
[C]: in function 'exit_cutscene'
level/freeplay.lua:122: in function 'handler'
core/lualib/event_handler.lua:47: in function <core/lualib/event_handler.lua:45>

I will try to look into this tomorrow. This should have been resolved already. Please try without other mods, and if the issue disappears add them one at a time until it reappears. Let me know if you have any other information on how to reproduce the issue.

Tried again to start a new game without Space Age, got a slightly different error this time:

Error while running event level::crash-site-skip-cutscene (ID 209)
The mod Builder Bot Start (0.4.3) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event BuilderBotStart::on_cutscene_cancelled (ID 179)
Unknown equipment name: fusion-reactor-equipment
stack traceback:
[C]: in function 'put'
BuilderBotStart/control.lua:192: in function 'EquipArmor'
BuilderBotStart/control.lua:240: in function <BuilderBotStart/control.lua:239>
stack traceback:
[C]: in function 'exit_cutscene'
level/freeplay.lua:122: in function 'handler'
core/lualib/event_handler.lua:47: in function <core/lualib/event_handler.lua:45>

For the first error, I had Mega Bot Start enabled as well, the second one does not have Mega Bot Start enabled. There's plenty of other mods on, I haven't yet tried removing them.