I never had an issue before, but this is persistent now:

The mod Realistic Reactors (3.1.2) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event RealisticReactors::on_pre_player_mined_item (ID 11)
RealisticReactors/scripts/heat/buffer.lua:64: attempt to perform arithmetic on field 'y' (a nil value)
stack traceback:
RealisticReactors/scripts/heat/buffer.lua:64: in function 'vecadd'
RealisticReactors/scripts/heat/buffer.lua:69: in function 'for iterator'
RealisticReactors/scripts/heat/math.lua:325: in function 'get_entity_neighbour_cells'
RealisticReactors/scripts/heat/network.lua:301: in function 'split_heat_network_cell'
RealisticReactors/scripts/heat/network.lua:533: in function 'remove_entity_from_network_cell'
RealisticReactors/scripts/heat/network.lua:637: in function 'remove_heat_pipe'
RealisticReactors/scripts/events/destruct.lua:56: in function 'on_heatpipe_removed'
RealisticReactors/scripts/events/destruct.lua:119: in function 'entity'
RealisticReactors/control.lua:61: in function <RealisticReactors/control.lua:59>

It also dies when I place a new heat pipe (I was trying to perturb the heat network to see if that would work around this case)
The mod Realistic Reactors (3.1.2) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event RealisticReactors::on_built_entity (ID 6)
RealisticReactors/scripts/heat/buffer.lua:64: attempt to perform arithmetic on field 'y' (a nil value)
stack traceback:
RealisticReactors/scripts/heat/buffer.lua:64: in function 'vecadd'
RealisticReactors/scripts/heat/buffer.lua:69: in function 'for iterator'
RealisticReactors/scripts/heat/network.lua:494: in function 'add_entity_to_network_cell'
RealisticReactors/scripts/heat/network.lua:628: in function 'add_heat_pipe'
RealisticReactors/scripts/events/construct.lua:35: in function 'on_heatpipe_added'
RealisticReactors/scripts/events/construct.lua:104: in function 'entity'
RealisticReactors/control.lua:51: in function <RealisticReactors/control.lua:50>

I don't know why yet, but it is most definitely caused by this mod : https://mods.factorio.com/mod/extended-descriptions

Thank you very much for the bug report!

Yes, this is a problem between big-data-string and extended-descriptions.
I filed a new issue over there:
https://mods.factorio.com/mod/extended-descriptions/discussion/6262f4cf06bc9f47b0984b00

Thanks!