Hi, I have a similar bug, not resolved by resetting up APN: 4G doesn’t work. 3G, LTE, 2G etc does.
I have two SIMs by two different operators. Both display only LTE, 3G etc, but not 4G. On a different phone both SIMs displayed “4G”, like my Fairphone 3 before update.
Whether the phone uses the term “4G” or “LTE” for the same thing might depend on the Android version or costumisations done by the phone vendor.
I would assume your phone after the upgrade would now simply display “LTE” in the situations in which it displayed “4G” before. You could check that at places where you know which kind of reception you got before.
This is still 4G working.
The difference in download speed is a different matter, the topic title should be “4G download speed slower” if the Fairphone 3 got 44 Mbps in that situation for you before.