The bug occurred a few seconds after placing a blueprint containing ghost on water entities, when placed in space with SE mod and scaffold platform automatic placement.

Log:
The mod Ghost On Water (0.12.0) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event GhostOnWater::on_tick (ID 0)
GhostOnWater/modules/waterGhostCommon.lua:36: attempt to index upvalue 'mask2' (a nil value)
stack traceback:
GhostOnWater/modules/waterGhostCommon.lua:36: in function 'func'
stdlib/stdlib/utils/table.lua:72: in function 'find'
stdlib/stdlib/utils/table.lua:89: in function <stdlib/stdlib/utils/table.lua:88>
(...tail calls...)
GhostOnWater/modules/landfillPlacer.lua:33: in function 'getLandfillType'
GhostOnWater/modules/landfillPlacer.lua:159: in function 'func'
stdlib/stdlib/utils/table.lua:116: in function 'each'
GhostOnWater/modules/landfillPlacer.lua:145: in function 'func'
stdlib/stdlib/utils/table.lua:116: in function 'each'
GhostOnWater/modules/landfillPlacer.lua:142: in function 'placeGhostLandfill'
GhostOnWater/modules/waterGhostUpdater.lua:96: in function 'handler'
stdlib/stdlib/event/event.lua:342: in function 'pcall'
stdlib/stdlib/event/event.lua:362: in function 'dispatch_event'
stdlib/stdlib/event/event.lua:438: in function <stdlib/stdlib/event/event.lua:396>

Can you tell me what other mods you have? I recall testing with SE and it seemed to work, but I only did some very simple tests with just SE, GhostOnWater and testing with some very simple single entity Blueprints.
I made a fix that some some extra check, which should fix the crash but it might not solve the underlying issue and result in some other problem.

Of course:

base_1.1.87
simhelper_1.1.4
VehicleSnap_1.18.5
aai-containers_0.2.11
aai-loaders_0.1.4
aai-signal-transmission_0.4.8
aai-vehicles-ironclad_0.6.8
Adjustable-Personal-Roboport-Range_0.9.0
alien-biomes_0.6.8
AutoDeconstruct_0.3.8
Bottleneck_0.11.7
bullet-trails_0.6.2
chest-auto-sort_1.0.0
CleanFloor_1.1.0
dynamic-robot-queues_1.0.2
even-distribution_1.0.10
flib_0.12.9
grappling-gun_0.3.3
informatron_0.3.4
jetpack_0.3.13
LogisticRequestManager_1.1.31
pump_1.3.3
Quicksave_0.3.0
robot_attrition_0.5.15
shield-projector_0.1.6
solar-calc_0.3.11
space-exploration-graphics_0.6.15
space-exploration-graphics-2_0.6.1
space-exploration-graphics-3_0.6.2
space-exploration-graphics-4_0.6.2
space-exploration-graphics-5_0.6.1
space-exploration-menu-simulations_0.6.8
Squeak Through_1.8.2
stdlib_1.4.8
textplates_0.6.10
combat-mechanics-overhaul_0.6.24
equipment-gantry_0.1.5equipment-gantry_0.1.5
Milestones_1.3.20
ModuleInserterER_5.2.5
puppy-vehicle-fuel-ui_0.1.1
RateCalculator_3.2.3
space-exploration_0.6.112
blueprint-sandboxes_1.16.4
GhostOnWater_0.12.0
resourcehighlighter-dark_2.5.0
space-exploration-postprocess_0.6.26

by the way, congratulations on your responsiveness and the quality of your mod

Did 0.12.1 fix it? It should a least fix the crash but it might cause landfill/scaffolding not to be placed at all or something. I won't have to look into this more if everything works fine now.