Magisk issue :Device rooted but Magisk not installed

Device: OnePlus7, Android 10

What happened

• Device was rooted with October security patch updated, custom kernel installed and Magisk Manager hidden (to prevent root detection by an app). All working fine. No problem.

  
  



• Updated Magisk Manager to 8.0.3 successfully but it shows Magisk not installed

  
  

• But device is properly rooted and all rooted apps work fine.

  
  



• I can see the hidden Magisk Manager in app drawer but tapping it doesn't help. Nothing happens. It tries to open, shows Magisk logo and disappears.

  
  



• I can't access the Manager menu to see if I can fix something from there.

  
  

What I tried

• Flashed Magisk again from laptop. No use.

  
  



• Restored stock kernel from backup made by kernel manager app. No use.

  
  



• As suggested by Didgeridoohan's guide tried these

  
  
  
  

  • Cleared data of Manager. Uninstalled and installed Magisk Manager. No luck.

    
    
  
  

  • Uninstalled manager, installed canary manager and set channel to update to canary hoping that may help. Doesn't help.

    
    
  
  
  
  

Device still properly rooted

• Saw this Github issue, Not applicable.

Things to try

• Flash Magisk uninstall zip and root again.

  
  



• Try manual patching of boot image and flash

  
  



• Dirty flash stock ROM - not possible because device is rooted and would result in boot loop.

  
  



• Any other simpler option?