When you change him is the absorbent part of the diaper soaked through, or just sort of wet?
Usually if the absorbent part is saturated, then you need to add more absorbency. If it's not saturated then you either have repelling and need to strip or you have a poor fit.
For repelling either try stripping with blue Dawn dishsoap or several hot water rinses with no soap.
I'm not familiar with how Alvas fit/adjust, but I will say that we used appleCheeks with our DS2 for three weeks with no issues. Then all of a sudden I had three leaks in one day. LO has recently started to move around more and he must have lost weight in his legs. I tightend the leg holes one snap & we're back to being leak free.