Look at your production history, you are probably having variable withdrawal rate.
For example, at the beginning of production oil rates were significantly higher and each year they dropping drastically. Thus, inflow from aquifer compensated and later overcompensated pressure decline from production. It is the case, when you are having low-permeability aquifer or bottom aquifer.

In my experience, I encountered tight oil field with aquifer, during first 5 years of production initial reservoir pressure declined from 300 atmospheres to 150 atmospheres. After that field was abandoned for 10 years, but there was small unofficial oil production from it (approximately 10 barrels a week). After 10 years when field started to be re-vitalized by another company, they discovered that reservoir pressure returned to its initial value – 300 atmospheres.