Cockling like that for a paper at 255 grams indicates to me that something is wrong with the paper coating. Usually there are 2 or 3 layers applied and one of them is a barrier to keep the ink media from penetrating the paper base or at least slows down that migration of the fluid so it will not create an issue on the printer like cockling. Or the paper may have been stored too long in different humidity conditions.
If there is an additional issue with the printer then it can be the head that is not set at the right distance from the substrate. Either by a media preset choice that is incompatible with the paper thickness or the hardware of the printer does not act properly. There is a small plastic part at the back of the head carriage that can be broken or the mechanism that shifts that part in and out for the head height is not working properly. I had the last problem on a Z3200 and exchanged the mechanism with the same part of a Z3100, must have been a connector issue as both parts and printers worked properly afterwards.
The plastic part is the Rear Carriage Bushing see
http://z3200.com/Rear_Carriage_%20Bushing-HP-Z3200_Printers-Mark%20Lindquist.htm Watch the Bob Wert video, it shows that mechanism too at 3.55
The mechanism that shifts it is precisely below the light grey insert/cup at the back of the right side cover. You can remove the right side cover. By placing back the ink cartridges you can start the printer again and watch what happens if you load a thick paper + its media preset versus a thin paper + its media preset. Alright, if you do not see that shift mechanism act then the connector of it may be the problem. Try to reseat it. The mechanism is that black part next to the screw the man in video unscrews at 3.55 in video time.
At a thick/thin/thick media change it holds the rear carriage bushing that works like a kind of wedge when the head carriage motor moves the head carriage to the left or the right. The rear carriage bushing knows just two positions and so there are only two head heights possible. If the head height is not adjusted properly it is that mechanism or the rear bushing broken.
You can even take the right cover off by simply setting the printer in cartridge replace mode and then take it off and set the cartridges back. That is how I do it but I have taken one screw away at the front/down/interior side and never use it anymore, hardest part of dismantling and construction wise not needed. Getting into the interior at the right goes fast then.
You can clip out the light grey cup of the right cover before you replace the cover etc again. That gives you a possibility to check that function for some time after the repair. The cup can be inserted again when everything is alright, it looks symmetric but is not so do not place it reversed. When still open I had a kind of trap there that showed whether the switch had worked or not. Tape and a small sheet of plastic foil resting on the black hook did it. You can figure it out.
Edit; at the bottom of that linked page the mechanism is shown too. But also how to oil the rear carriage bushing on the lubrication sponge. Which may prevent an error warning that could result in replacing the maintenance station in total. I had that error but figured out it had more to do with the head carriage not moving fast enough from the maintenance station when initialising so I oiled the bar and that spot and the error disappeared.
Met vriendelijke groet, Ernst
http://www.pigment-print.com/spectralplots/spectrumviz_1.htmMarch 2017 update, 750+ inkjet media white spectral plot