I recently built a profile for Ilford Gold Fibre Silk using Bill Atkinson's 1728 patch target. The prints that I am producing are darker than I would expect from softproofing results. Today I printed an image using the canned Ilford profile and mine. Softproofing shows them looking identical but the canned Ilford profile is lighter and much closer to what I see on the monitor.
Plan A is to print the targets again and then remeasure and build a new profile. My assumption is that I did something wrong along the way when building my profile. What has me rattled is that the monitor looks the same for both but the results are quite different.
Assuming there is no double profiling going on, there is no reason I can come up with as to why two softproofs should look identical while the prints differ. Is it possible that one was either softproofed or printed with a mismatch in rendering intents? Could one of the profiles be optimized for a different viewing color temperature? Is it possible that your homebrew profile is damaged?