(This option differs from renaming of feacp.dll, in that setting value to "Disable" still causes the IDE to load an existing NCB.) Note: Visual Assist ignores value of registry string value "Default Intellisense" if option to "Get content from default Intellisense" is enabled.
If for some ODD reason you want to disable Intellisense in SQL Server Management Studio, there is a very easy way to do so.
You might also want to edit your question and break it up into some readable paragraphs; the wall of text you posted is hard to read, and the easier you make your question to read the better your chances of getting help.
One solution is simply to close the page and re-edit it.
Here's some KBD shortcuts to try to reboot it, but don't know if they work. I had the same issue, it turned out to be that nuget packages were not automatically downloaded for a solution i downloaded from the repository freshly, thus intellisense was not available since none of the required packages to show the right suggestions were available.
it will give you intellisense I had the issue in just one file.
After creating the new class and working on it, it hadn't been added to the scope of my project.