Have you hooked your accolade devices up to anything ?,
When using them there is a calibration process, which can take a fair while, this happens so your XP awards are adjusted to suit the amount that they should be getting for that much playtime.
In this case the XP is then awarded in the fortnite lobby, but not straight away on return to lobby. UEFN maps without accolade devices also have XP awarded in the fortnite lobby, sometimes an hour or so after they finish playing that map.