Most of my lipos behave in a similar manner.
The maximum charging voltage is between 4.20 and 4.23-4.24 as shown on the charger's display.
After setting a few minutes, the voltage typically drops to between 4.18-4.19.

The charger's adjustments and settings for "dead band" and "offset", as well as C/10, C/20, and accurate, quick, high current, etc. also impact the
difference.

If I were to set the charge rate to a lower than normal value, say 10% of normal, and also select accurate,
The voltage difference between the charging voltage and the at rest voltage will be less. The C/20 setting can also reduce the difference.

Why? It seems that the lower charge current setting also lowers the minimum current for final charge and balance. The C/20 setting
also lowers the minimum current.

Many chargers can measure the voltage difference between the voltage when charge current is applied, and when it is not, then using the difference to
alter or terminate the charge.