I'm sure you're not doing anything wrong. In fact I seem to remember that we may have fixed a bug specifically to do with calculation of groundspeed during prolonged climbs. In the latest beta build (which you can download yourself to test if you like) the first leg of that route comes out as GS 82kt, time 14min. This is an average; according to SkyDemon the initial climb covers about 60% of the leg from Blackbushe-HAZEL.

Ok, good idea, let me try ... here we go:

default aircraft, no wind, route Blackbushe-HAZEL-LA(NDB near Lyneham)-Bristol, at 6000ft;thus EGLK-HAZEL is entirely climb, and SkyDemon PLOG for that first leg is:
Dist:20nm
GS:113kts
Time:11min
which is consistent (Dist / Time = GS)

however, the climb speed of the default aircraft is 79kts IAS as per the set-up menu, which even at 6000ft will only be roughly 89kts TAS (using 2%/1000ft rule of thumb); the aircraft is entirely in the climb to HAZEL so must be 89kts or below, which would seem to conflict with the 113kts in the PLOG (?)

as an aside, looking at the HAZEL-LA leg, the GS is 118kts, so per the PLOG the aircraft would be almost as fast in the climb as it is at cruise level, which just intuitively feels odd

it may well be that I'm entering or reading something the wrong way, and it's not a huge discrepancy to be relevant for most flights (certainly at lower altitudes it isn't, I only stumbled across it when planning a FL090 cruise), I was just puzzled ... hope this helps

I can tell you that the GS displayed in the PLOG is the average groundspeed achieved over the whole leg, which in a climb will be slower. If you find a specific example that it's easy to recreate where this doesn't appear to be reflected, we'll be happy to go over it with you.

I'm stumbling over the calculation of the groundspeed and time in the PLOG. It seems to calculate the GS at the end of the leg, and use that to calculate the time for this leg. However, if it's a longer climb (say FL90), then for most of the time during the leg the GS will be significantly lower, and thus the time required for the leg significantly longer that what's in the PLOG.
Have tried it with a PA28 climbing up to FL90 and back down over roughly 40nm, and the PLOG shows 20mins req'ed for the climb leg, with a GS at FL090 of 130-ish kts, whereas climb speed is actually around 80kts and thus timing should be closer to 30mins (bit less as TAS increases with height).
Am I missing something?
Many thanks.