Handicap increase despite shooting below (net par)

Hi all

I suspect I know the answer, but I'll lay out the scenario.

I don't play competition golf, but instead record all rounds on the EG app with another player attesting them.

I played yesterday off 8.6 but only 8 shots given according to the app when I started my round. I shot a +6 gross round (IE 2 under) so was expecting a small cut, instead I went up .3 to 8.9

my assumption is that other scores were put in that day by other members and the course was playing easier that usual.

any thoughts/input greatly appreciated.