Thanks for trying to help and sorry for the late reply.
Yes, it seems I should clean the rollers. However, those instructions are not useful at all. Instax camera rollers are not as easy to clean as Polaroid's. At least in the Instax 100 they seem to be sealed while the film is not being ejected.
I'm hating Fujifilm right now. The manual is a useless and cumbersome piece of paper that says nothing about cleaning the rollers and how to do it. It seems the only way to do it is pushing the shutter button without film and cleaning while the door film is open, which is a waste of batteries. There is little info on the web about this.
In addition to the chemical stations, all the pictures had white stains in the picture. The white (undeveloped?) stains matched some "pits"on the back as if something was punching the picture while ejected.
So what did I do? I put the camera in a room with very little light, put the camera in a dark bag and removed the cartridge. Then I cleaned an horizontal metal bar that is located between the lens and the film ejection door. It was very dirty. I used alcohol (stupid me; the manual says I shouldn't use alcohol). Of course, after putting the carriage back, the next picture came undeveloped as the camera was expecting a dark side. Another picture wasted. Then the punches and white stains did not appear in my next test shot but the chemical lines all across the whole paper are more visible than ever. Damn! I hate it even more because the lines had become less visible shot after shot although they were still there. It seems that removing the cartridge and putting it back took the problem back to square one.
(Sorry about the image. I'm not good at selfies and don't have a great body either)
So I'll have to waste this cartridge and try to clean the rollers before loading the next one.
I was planning to buy a second hand Instax Share Sp-1 or an Instax Mini. Are they so troublesome and hard to clean as the Instax 100?