Glow and potential?

Je
I've been tracking with Glow since October but went back over my period dates from April. I average around 28days for my period. 
Now I'm not actively trying to get pregnant , but I do pay a little attention to the ovulation dates especially as I've been in a LDR and trying to pay more attention to my cycle. 
I'm now on day 36, negative hpt
All of a sudden the <a href="https://play.google.com/store/apps/details?id=com.glow.android">Glow app</a> has changed my ovulation period to take into account of my delayed period. The highest % of pregnancy now covers when I did have sex, so now I'm concerned. 
How accurate has the <a href="https://play.google.com/store/apps/details?id=com.glow.android">Glow app</a> been for you in <a href="https://play.google.com/store/apps/details?id=com.glow.android">tracking ovulation</a>? 
Personally I've been under a lot of stress. So think this is more likely the cause but still...