Oops sorry, seems I misead about wakings in early evening, probably cause ours were due to UT.
Walkings could be related to the solids. What time are you giving them? Arching back could be discomfort. It has taken 2 weeks for Aaron to settle down after weaning. For Aaron I have found I cannot give solids later than 4.30 pm. I space milk and solids through the day so solids tends to be 1 hr after milk. Everytime I have introduced a new food it unsettled him for 3 days, but he does settle. I have read lots that weaning causes NW as it is very stimulating, and that was certainly the case for us and just starting to get back on track now.
Did he seem OT at first nap and how did he wake. DS often wakes happy or at least not too grumpy at 45 mins from UT nap and screaming if OT. I often can't tell until wake up. this morning DS has UT short nap, but had been grumpy for 45 mins before bed, only now can I see it must have been discomfort. I would be tempted to stick to A time of 2hr 15 for a couple of days before you change anymore. Give him a chance to get used to that first, unless he shows obvious signs of being able to push it.