Normally this can happen if there is a voided bet which usually comes about through VAR decision, although there doesn't look like there was one in the first half
If you post your matched bets from Betfair and from Bet Angel and the Bet Angel log from that market we should be able to piece it together
Also how many markets do you have in Guardian and what refresh rate are you using?
and are you using Streaming or Polling to fetch price updates?
btw, i've moved your message to its own thread as its wasn't related to the release topic originally posted in