Pressure buildup data should always be examined for #welltest analysis (#PTA) quality control and anomalies.
Several phenomena might cause data anomalies immediately after shut-in. Phase redistribution (gas going back into solution) can cause a hump in the early-time data. Liquid fill-up can cause a drop in pressures (changing from gas above the formation to a liquid head). A falling liquid level may cause a sudden increase in pressures, as the column between recorders and formation changes from liquid to gas.
One might also observe liquid shifts well into the buildup. Other completion operations (i.e. on an up-hole zone) may affect the buildup, which could suggest communication behind pipe, across a packer, or through a leaking plug.
Longer term one might see shut-in pressures start to decline, suggesting communication or interference from offset producing wells or isobaric pressure gradients due to drainage.