Automated Sorting and Grouping VBA

Hi guys,
even though I have been on this site many times and it was great help in solving VBA problems, this is my first post here.

The thing, is a supposed to develop a project management tool, which automatically adds new tasks and in the list, sorts them accordingly and then groups them depending on the categories. By that I mean, 1.0.0. is the main category, 1.1.0. is sub category etc...

I have found a helpful macro on this site regarding grouping and other parts I have put together with writing and recording the macros.
I admit, it is not the most elegant way how to deal with it, but was the only way know.

The problem is, after some time, the sorting function stops to work for some cells and i cannot find the origin of this issue.
Can you please have a look at this problem. The file is attached.

P.S. The strange numbers (999999999999999999999) at the end of the list are there to set the border for grouping macro.

Thanks a lot,

Ivan