At the moment we are trying to rule out the obvious so please bear with me, some checks to do below, one at a time please;
Windows normally allocates the size of the page file automatically, typically one and a half times the physical memory that is installed.
Please try making the minimum box 12GB and the maximum 18GB.
Create a new restore point first then see below;
Open My Computer. At the top right, there is a search field...type pagefile.sys and click the search icon. In the search results, right click on the file (pagefile.sys) and choose Delete...confirm the deletion.
Restart your machine. A new pagefile will be created automatically when the machine starts.
Try running Windows own memory testing tool, details here