That was quite a jump in volume and probably the consecutive nature of your running means your body might not be recovered. I would look to have another rest day and maybe make a couple of the 10kms into 12-15s at a slower pace.
My progression over the last few weeks:
19.9km
22.7km
21km
25.9km
29km
32.6km
36.3km
Everyone's different and has different aims but your weekly increases seem insane to me.
Also, there's not much point benchmarking yourself against a race time, when you're so badly rested, using HR as the metric.
Are you running the same or similar loop? And the aim is just to run for distance @ 10km?
If that were me I’d be a bit bored, so might run slower. You’re probably also tired so running slower.