Interpolation maps registered

[alexyork]

Check that there are no materials with interpolation used in your material slots. Sometimes these get left behind.

[jacksc02]

All cleared out (by habit)
Even with all of the geometry deleted and just leaving the materials in the slate material editor the file is 326mb in size. So i think there is something being left behind in the scene that is causing issues.

[tashko.zashev]

Here is the ticket number and subject -
[#858015] Interpolation maps issue

Found it, thank you. One of may colleagues is investigating the issue now.