Question Unity Sourcetree Plugin namespace reference error infinity loop

Hi! I have basic understanding of using Sourcetree and Unity. I'm working with my colleague on a VR project that features 2 players in the same virtual room, for which we're using Photon. We're also using FMOD, Oculus, DOTWEEN, FMETP_STREAM and Sirenix.

We have a rather detailed gitignore, possibly too detailed?

Code (CSharp):

1. # This .gitignore file should be placed at the root of your Unity project directory
2. #
3. # Get latest from https://github.com/github/gitignore/blob/master/Unity.gitignore
4. #
5. /[Ll]ibrary/
6. /[Tt]emp/
7. /[Tt]emp.meta
8. /[Oo]bj/
9. /[Bb]uild/
10. /[Bb]uilds/
11. /[Ll]ogs/
12. /[Uu]ser[Ss]ettings/
13. /[Mm]emoryCaptures/
14.  
15. # Asset meta data should only be ignored when the corresponding asset is also ignored
16. !/[Aa]ssets/**/*.meta
17.  
18. # Uncomment this line if you wish to ignore the asset store tools plugin
19. # /[Aa]ssets/AssetStoreTools*
20.  
21. # parrelsync not needed for Jorick:
22. # /[Aa]ssets/ParrelSync*
23.  
24. # Autogenerated Jetbrains Rider plugin
25. [Aa]ssets/Plugins/Editor/JetBrains*
26.  
27. # Amplify not needed for Jorick
28. [Aa]ssets/AmplifyShaderEditor*
29.  
30. # Visual Studio cache directory
31. .vs/
32.  
33. # Gradle cache directory
34. .gradle/
35.  
36. # Autogenerated VS/MD/Consulo solution and project files
37. ExportedObj/
38. .consulo/
39. *.csproj
40. *.unityproj
41. *.sln
42. *.suo
43. *.tmp
44. *.user
45. *.userprefs
46. *.pidb
47. *.booproj
48. *.svd
49. *.pdb
50. *.mdb
51. *.opendb
52. *.VC.db
53.  
54. # Unity3D generated meta files
55. *.pidb.meta
56. *.pdb.meta
57. *.mdb.meta
58.  
59. # Unity3D generated file on crash reports
60. sysinfo.txt
61.  
62. # Builds
63. *.apk
64. *.unitypackage
65.  
66. # Crashlytics generated file
67. crashlytics-build.properties
68.  
69. # Mac stuff
70. .DS_Store
71. .bak
72. .BAK
73.  
74. ### FMOD Unity Integration ###
75. # Never ignore DLLs in the FMOD subfolder, so make sure that the FMOD-folder is in the correct path.
76. !/[Aa]ssets/Plugins/FMOD/**/*.dll
77.  
78. # Don't ignore images and gizmos used by FMOD in the Unity Editor
79. !/[Aa}ssets/Gizmos/FMOD/*
80. !/[Aa}ssets/Editor Default Resources/FMOD/*
81.  
82. # Ignore the Cache-file since it is updated locally either way
83. /[Aa]ssets/**/FMODStudioCache.asset
84. /[Aa]ssets/**/FMODStudioCache.asset.meta
85. [Aa]ssets/Plugins/FMOD/Cache.meta
86. /[Aa]ssets/Plugins/FMOD/Cache/Editor.meta
87.  
88. # Log-files
89. fmod.log
90. fmod_editor.log
91.  
92. # FMOD 1.10.x (Legacy)
93. /Assets/FMODAssets/*
94. /Assets/FMODStudioCache.meta
95.  
96. #Odin inspector
97. # Ignore the auto-generated AOT compatibility dll.
98. /Assets/Plugins/Sirenix/Assemblies/AOT/*
99.  
100. # Ignore all unpacked demos.
101. /Assets/Plugins/Sirenix/Demos/*
102.  
103. # But keep the demo packages themselves.
104. !/Assets/Plugins/Sirenix/Demos/*.unitypackage
105.  
106.  
107. Assets/Photon/
108. Assets/Plugins/
109. Assets/FMETP_STREAM/
110. Assets/Oculus/
111. Assets/Demigiant/
112. <<<<<<< HEAD
113. Assets/Photon.meta
114. =======
115. Photon.meta
116. >>>>>>> b4d66b80e8f59dc327ca26196082dfe3e4d4a478
117. Assets/FMETP_STREAM.meta
118. Assets/Oculus.meta
119. Assets/Plugins.meta
120.  

We've established that keeping these plugins from the gitignore list caused a multitude of weird conflicts.

Right now, we seem to be stuck in a loop that when my colleague or I pull in or merge another's commit, Unity spews out hundreds of CS0246 errorcodes: "The type or namespace *INSERT ANY* could not be found.." of files related to those plugins.
These errors are then fixable by reimporting the plugin files from a backup, yet this action is also what seems to keep the loop alive; Sourcetree will notice this action, regardless of it being on the gitignore. Since we're trying to keep this plugin stuff away from version control, we do Stop Tracking when these "changes" arise in a new commit and Discard when these "changes" are pulled or merged. Since all of it is on the gitignore list, how come it doesn't actually ignore the changes made to these files, regardless of them having the same name and path as listed on the gitignore? Seems of (presumably) little relevance, but I work on mac, while my colleague works on PC.

It feels like we're using git the wrong way, even after literal months of looking into this problem. We've spent too many days reimporting, looking up the issue online and coming up with solutions and failing, but it seems we're just stuck. Help is really much appreciated!

Side question: how does that <<<<HEAD>>>> part in the gitignore list change gits behaviour?