I'm also seeing errors while using the plugin. I can pretty reliably recreate the issue by opening multiple models with ThruPain open, then switching between them. Once it has an error the plugin becomes unusable. I've also had it fail in other contexts, for example, working on a single model, but those are tougher to recreate reliably.

Video Showing Repro
ThruPaintErrors.mp4

Plugin information for Support

Fredo6 Plugins Information on 2024-09-29 07:34:40 -0400
--------------------------
- Platform: arm64-darwin - Ruby: 3.2.2
- Sketchup: 24.0.595
- LibFredo6: v14.6a
- LibFredo6 Binary loaded
- Sketchucation ExtensionStore: 4.4.0
- SCFLicense: v6.4a - 72
- Fredo6 Plugins
- SCFLicense directory present
    > Signature File: 2024-04-19 21:52:41 -0400
    > ClothWorks: 2024-02-12 20:32:28 -0500
    > ThruPaint: 2024-09-26 07:53:53 -0400

Errors Observed
First Error when switching between models

Error: #<NoMethodError: undefined method `each' for nil:NilClass>
/users/jusbell82/library/application support/sketchup 2024/sketchup/plugins/fredo6_thrupaint/bootstrap_thrupaint.rbe:397:in `exit'
/users/jusbell82/library/application support/sketchup 2024/sketchup/plugins/fredo6_thrupaint/bootstrap_thrupaint.rbe:302:in `model_activating'
/users/jusbell82/library/application support/sketchup 2024/sketchup/plugins/fredo6_thrupaint/bootstrap_thrupaint.rbe:283:in `onActivateModel'

Subsequent errors when trying to activate tool via toobar.

Error: #<NoMethodError: undefined method `[]' for nil:NilClass>
/users/jusbell82/library/application support/sketchup 2024/sketchup/plugins/fredo6_thrupaint/thrupainttool.rbe:547:in `paint_mode_change'
/users/jusbell82/library/application support/sketchup 2024/sketchup/plugins/fredo6_thrupaint/bootstrap_thrupaint.rbe:422:in `execute_direct'
/users/jusbell82/library/application support/sketchup 2024/sketchup/plugins/fredo6_thrupaint/bootstrap_thrupaint.rbe:79:in `action__mapping'
/var/folders/85/65t6bh0j5gb1ntqbpx3_20dm0000gn/T/com.sketchup.SketchUp.2024.jusbell82/Fredo6_LibFredo6_TemporaryFiles/data6.rb:65:in `call'
/var/folders/85/65t6bh0j5gb1ntqbpx3_20dm0000gn/T/com.sketchup.SketchUp.2024.jusbell82/Fredo6_LibFredo6_TemporaryFiles/data6.rb:65:in `launch_action'
/users/jusbell82/library/application support/sketchup 2024/sketchup/plugins/fredo6_!libfredo6/lib6plugin.rbe:244:in `launch_action'
/users/jusbell82/library/application support/sketchup 2024/sketchup/plugins/fredo6_thrupaint/bootstrap_thrupaint.rbe:69:in `launch_action'
/users/jusbell82/library/application support/sketchup 2024/sketchup/plugins/fredo6_thrupaint/bootstrap_thrupaint.rbe:145:in `block in startup'
/users/jusbell82/library/application support/sketchup 2024/sketchup/plugins/fredo6_!libfredo6/lib6plugin.rbe:1463:in `command_invoke'
/users/jusbell82/library/application support/sketchup 2024/sketchup/plugins/fredo6_!libfredo6/lib6plugin.rbe:1443:in `block (2 levels) in build_config_commands'
/users/jusbell82/library/application support/sketchup 2024/sketchup/plugins/fredo6_!libfredo6/lib6traductor.rbe:1446:in `block in add_command'