The difference between 7 and 8 or 6 is minimal. Very little change in the composition lets the pH drift around 7. From 7 to 8 it would mean adding only 10-6mol/L of a strong base for instance. Drifting by one unit around 2 or 12 would require a much bigger composition change.
Organic materials react among themselves, from ageing, with air, with light... I feel pretty much normal that the pH drifts.
Imagine that the solution (or suspension?) contains 0.1mol/L of dissociated acids, of which 10ppm react with ethanol over a day, you get already the 10-6mol/L drift. It's more complicated because these acids aren't fully dissociated, nor can I guess if a reaction with ethanol is the cause, but the idea is that many reasons can let the pH drift around 7, this process is pretty normal, preventing it looks unnecessary and extremely difficult.