Physio True-up

the same for me ! did a 2h ride with my edge 1030 : TE aerobic : 3.1 anaerobic 2.2 load reported by the 945 : around 20 ... in grey
did a small jog 1/2h with the 945 load 46 ! 

When Physio True-up was first introduced there was some wonkiness where even though you had enabled it during set up it didn't register and you had to disable & sync and re-enable & sync it before it started working right. Try doing that with the watch first and then your Edge if doing just the watch didn't work.

It's worked without having to go through that step with my subsequent Garmin buys but if this is the first time you've had 2 devices with this feature it might be the problem.

i have also experienced the same issue.

I had a 935 before that and it worked just fine, I also have the Edge 130. I'll try to de activate and reactivate it anyways but  the problem isn't that it's not syncing, it's that it syncs but the 945 badly calculates the load

What actually is the issue? Is it really Physio TrueUp or the fact that the 945 has (I believe) updated First Beat code and so likely to produce differing load scores. I guess the best test of this is to use both an Edge 1030 and a 945 and compare the exact same activity. Often running will give far higher "stress" scores due to the weight bearing nature of running. 

For instance I did both the running and cycling version of the Giro prologue on Zwift. For the running one I got a Load of 188 but only 99 on the bike both measured on the 945. OK not a totally ideal comparison as was trying more on the run but an illustration that running likely to produce somewhat higher scores

That said I did an 800 race last night on the track and got a load of 71. It was "harder" than that bike ride even though only 2:25.1 of effort.

issue is that 945 doesn't either "reports" or "calculates" the righ values for an activity that comes from another device. It reports good values if the activities come from the 945 but true up doesn't work properly then as explained here.
Of course your giro prologue was harder while running, it's the same number of Km by bike or run, it was faster biking ! 

Physio True-up is a big reason I've decided to use the 945 for everything. Sold my 520+. It just never worked properly, and the metrics you receive from 945 are better than what you get from the 520+.

Does the 520+ support Extended Display? If it does then you could still at least have a larger and better placed view of the your 945 stats while riding.

It does, I tried it. Doesn't support connect IQ data fields which I have to use to show more metrics. 

I've riden a few times with the 945 in the quick connect mount and it is good enough. No need to worry about 2 devices with charging, powering on/ off, syncing, buggy firmware.

Trying the simple life..

Similar problem here. Did a MTB ride on my Garmin 1000 which uploads to GC but doesn't show on 945.

Eventually managed to get the ride to show on 945 by disabling Physio TrueUp and syncing multiple times, restarting and then reenabling TrueUp. Took quite a few goes though.

Still doesn't count towards training status or intensity minutes on the watch or in GC. Something must be wrong, not calculating TE or other things is a pain, but not even updating the intensity minutes total when you have time in HR zones seems very wrong.