Abnormal heart rate detected! 3 times in an hour whilst not exercising. A bit scarey. Have finally managed to download music through ap on computer as couldn't get android phone to establish wi fi.Urgent visit GP am if this is true! Help

i had this with 6.20 a few times, it was wrong! was sat having a pint one of the times!

Never happened with previous firmwares.

I have a resting heart rate of 40

Check your alert threshold setting.  Long press on the HR widget/ heart rate settings/  tap on abnormal heart rate (words not switch) & then set alert threshold.   Mine has has reset to zero once or twice since the feature went live after an update.  (VA3 ) Hope that helps.

Didn't know about that, what do you think it should be set at? was on 0

It will be different for everyone.  I looked at my average resting HR (usually 50s -70s  & set mine to 110)  The only time it tripped after that is when I was eating very spicy food.  This article might explain it a bit better

https://www.garmin.com/en-US/blog/general/setting-alerts-for-abnormal-heart-rate/ 

I think when it is set on zero just about having a heartbeat will trip it.