dynamic block slowing down drawing

[drafting.82475]

Hi All

Thank God is Friday.
I am facing an issue with one of the dynamic blocks that our civils guys use to set out slab/exterior levels on housing developments engineering drawings. I will try to explain and will attach 2 samples.
The block is dragged into the drawings from a tool palette, then the slab levels attribute is set (user input) all other levels are automatically set by fields and formulas to get the other levels (exterior, threshold). There is a visibility state that provide none or additional levels to cover various situations/layouts.
Our problem start when we have a large number of this specific block on drawings, the engineering drawing become extremely slow on saving/autosave (+15s on a 6Mb drawing) as well as overall lagging on pretty much any operation. I have extensively researched that internally using various engineering drawings and I am certain that this block is the culprit, to the point that on more than one drawing I have exploded all instances of that particular block and the problem has disappeared.
For the life of me, I can’t understand why this block is causing that, every trick in the book has been tried (purge, audit, Regapps purge, various system variables settings etc). The 2 files attached show the block dragged into a clean file 10 times only (drawing3) and with a much larger number of instances on the other one (drawing2) and you can see how drawing2 is a lot slower from opening.
I would appreciate if the clever minds that make this Forum so valuable could show me a way to fix this problem, it is a very valuable tool to the guys working on a daily basis and we would like to keep using it.
Software / Hardware background
All workstations on the network are Windows 10, using either AutoCAD 2017 or Civil 3D 2017 (we still have not managed to merge to the 2018 because of the UKIE template. Shame on Autodesk).
All workstations are Core 7 with +32Gb RAM and SSD disks.
Thanks in advance for any suggestions/ideas and you all have a great weekend.