Hello, I noticed this issue with Premiere Pro 2020, the version I tried is 14.3.2.
Take a regular cube LUT, name it lut.cube, and put it in your Custom Technical LUT Folder: c:\Users\#USERNAME#\AppData\Roaming\Adobe\Common\LUTs\Technical
Take another LUT, name it lut_2.cube, and put it in the same folder.
Start up Premiere, and choose lut.cube from the Lumetri input LUT list (do no use browse, use the list)
Once it is applied, try to choose lut_2.cube from the same list. It will not be applied. Rename lut.cube to lut_1.cube and the issue goes away. As long as the first LUT has a name that matches the start of the second LUT, the second LUT will not be applied.
This was not an issue in Premiere Pro 2018, it appeared sometime later.