I installed the portable version (from Scoop) of MikTeX 2.9.6615-x64 on Windows 10 (as I did before with previous Miktex versions).
When I try to add a custom texmf directory for local packages in the MikTeX Console, it shows among the default paths (just above the default Install directory, as intended), but it disappears after I close the MikTeX Console. In other words, it doesn't store the change in the directory list.
My texmf directory worked in previous MikTeX version, and has the following structure: ../tex/latex/$packagename$
I tried the same with the old GUI, but the result is the same.