I get an error since today:

Error while running event mining-patch-planner::on_research_finished (ID 18)
LuaGuiElement API call when LuaGuiElement was invalid.
stack traceback:
[C]: in function 'index'
__mining-patch-planner/gui/gui.lua:163: in function 'create_setting_selector'
mining-patch-planner/gui/gui.lua:1220: in function 'update_quality_sections'
mining-patch-planner/control.lua:284: in function <mining-patch-planner/control.lua:269>

Could I have a save file where this happens?

This happens in my save as well. It triggers upon completion of the Quality Module research.

Link to the save: https://file.io/pKxEXdykV3g5

Released an update that should fix it.

I just downloaded the new version and the same thing happens.

The mod Mining Patch Planner (1.6.19) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event mining-patch-planner::on_research_finished (ID 18)
LuaGuiElement API call when LuaGuiElement was invalid.
stack traceback:
[C]: in function 'index'
__mining-patch-planner/gui/gui.lua:163: in function 'create_setting_selector'
mining-patch-planner/gui/gui.lua:1220: in function 'update_quality_sections'
mining-patch-planner/control.lua:286: in function <mining-patch-planner/control.lua:271>

Sorry about that, missed an edge case in which MPP is the only updated mod, released version 1.6.20 that should actually fix it.

That fixed it. Thanks!

The bug is still present, I run version 1.6.20 of the mod on my server.

I just downloaded the new version and the same thing happens.

The mod Mining Patch Planner (1.6.19) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event mining-patch-planner::on_research_finished (ID 18)
LuaGuiElement API call when LuaGuiElement was invalid.
stack traceback:
[C]: in function 'index'
__mining-patch-planner/gui/gui.lua:163: in function 'create_setting_selector'
mining-patch-planner/gui/gui.lua:1220: in function 'update_quality_sections'
mining-patch-planner/control.lua:286: in function <mining-patch-planner/control.lua:271>

But the crash log says 1.6.19? Can you give me a save file, please?

There's my savefile : https://www.mediafire.com/file/ab28ws60ntycg14/Space_Age.zip/file

To reproduce, research "Modules" then "Quality Module".

I am getting the same:

The mod Mining Patch Planner (1.6.20) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event mining-patch-planner::on_research_finished (ID 18)
LuaGuiElement API call when LuaGuiElement was invalid.
stack traceback:
[C]: in function 'index'
__mining-patch-planner/gui/gui.lua:163: in function 'create_setting_selector'
mining-patch-planner/gui/gui.lua:1220: in function 'update_quality_sections'
mining-patch-planner/control.lua:286: in function <mining-patch-planner/control.lua:271>

My savefile is at https://drive.google.com/file/d/1sP81i3JaBoX18DsXfS1CvN5w3tAZPxgO/view?usp=sharing and is about 5 seconds prior to the crash

Thank you for the save files, released update 1.6.21 that fixes the problem.