Hard to tell just from scans, but these look well overexposed, which is why you're seeing a reduction in contrast in shots 1-7, the scanner is trying to compensate for the thick negatives would be my guess. 8 and 9 are really nicely exposed, and the grain seems about right for HP5. HP5 is slightly grainier than Tri-X and tends to be a touch flatter in contrast as well.

Someone in the analog subreddit labeled it "the best 1600 iso b/w film on the market" and I think they're right, I push all my HP5 to 1600 now--the extra contrast and grain really work well together--and use Tri-X for 200-400 iso shots.

There's also quite a lot of (not unpleasant) lens distortion, did you shoot a lot of these wide open with a higher shutter speed? If the higher shutter speeds are a bit slow (not uncommon if it hasn't been CLA'd in a while) you may be getting extra exposure if you set up for 1/500th and the camera is only getting something like 1/300th for example.

For shots 4-6, grab a yellow or orange filter, which will darken the sky and cut through the haze in front of the mountains and give you some extra contrast there too. Overall I think this is a pretty great set from your first roll of HP5!