I perfectly know it's just a line level signal, but I have this problem only with the load box, I tried what you describe. My Global Settings are like Schmalle said and I tried to use the return input instead of the main one that I normally use but the result is the same. I can post a preset for sure if you feel like it could be helpful, but honestly you can totally replicate it quicker because I use just one block (IR 2048), mix 100%, the level of the block just raises the processed sound (of course I tried it at 0dB) but it doesn't affect the Dry bleed level in any way so that's still present. It does it with every Impulse Response I use, of different brands too.
You're right, it's only a line level signal and it doesn't appear to show the problem when used in my amp FX loop. I'm scratching my head because the chain is so simple (GTR > AMP > LoadBox > HX > PC Interface) that I can't understand why it's not working properly.
@SimonGugala Thank you and good luck to you too!