Delete operation on Sequence mode causes hanging bonds and undeletable monomers

[AlexeyGirin]

Steps to Reproduce

1. Go to Macro - Sequence mode (clean canvas)
2. Load from KET: Delete operation on Sequence mode causes hanging bonds and undeletable monomers.zip
   
3. Select monomers as shown on the picture and delete them
   

Actual behavior
Since that moment on flex mode hanging bond appears:

On sequence mode undeletable chem appears:

Expected behavior
No hanging bonds and undeletable monomers

Environment details:

• Ketcher Version 3.4.0-rc.1 Build at 2025-05-08; 12:13:14
• Indigo Version 1.32.0-rc.1.0-g65e26e370-wasm32-wasm-clang-19.0.0
• Chrome Version 136.0.7103.93 (Official Build) (64-bit)
• Win10

Related issue: #6254

[mobilisf]

Bug reproduced.

Environment:

• Ketcher Version 3.4.0-rc.3 [Build at 2025-05-15]
• Indigo Toolkit Version 1.32.0-rc.2.0-g94ab270bd-x86_64-linux-gnu-11.2.1
• Chrome Version 136.0.7103.114
• Win11