You could be suffering from "refreshed ears" syndrome. It happens to me all the time. You play a certain tone all day long, then go to bed, and only to wake up the next day and swear someone touched your stuff! It's because your hearing was refreshed during sleep --and you begin the cycle all over again.
I've actually had to go back and track over a mix just to prove to myself the tone hasn't changed.
I suffer from this badly. My ears adjust to a sound almost instantly. If I play for more than a few chords my brain dials it as perfectly flat. Ever since I bought the Kemper I have started it everyday and said "This does not sound like it did yesterday". And it is really making me aware of all the variables of tone so much.
The best solution is to get some golden standard so you know what a certain profile should sound like. Since I normally play thru my PC audio device, I have a couple songs ready to go as reference. But a trusted profile would be great also.
I also find myself adjusting my playing to a certain profile. For instance a profile that has huge frequency dips and sounds like you are playing in a tube/small room I tend to not play full chords where I can hear that freq suck out.
Another problem is what you are listening to the profile on and where you are standing when you hear it. If your speakers/system are not perfectly the same for all volumes you will get tonal differences from the volume change. If you dont stand in the exact same position as last time some freqs will be missing or phase canceled by the room and/or your other speaker if stereo.
Headphones may help with repeatability but are more prone to fatigue. So probably not?
And louder is always better to us humans. If yesterday you played it loud. Today you played it quiet. It will sound completely different to your ears.
Or maybe. Just maybe. Kemper has gone so far in their tube mimicking software that the Kemper acts like real tubes and changes continuously