Based on your last update, I'd look at two potential problem areas:
Re tight restrictions: Have you given him a pathway to earning his privileges back? Or if the "tight restrictions" are the norm (for example, some families have strict policies on screen time), have you given him a pathway to earning extra rewards for positive behavior? If he feels like he's got nothing to gain or lose, then there's no external reason for him to change his behavior.
With our DD7, whenever we take away a privilege, we either set a deadline for when she'll get it back (further violations reset the timer), or we tell her a behavior she can demonstrate to get it back. For example, if she can make it through a day/week without doing X, she gets it back.
And on the flip side, rewards, which can be extra privileges, or something else she values. For example, our DD was recently pulled out of school for homeschooling, and was having daily meltdowns with anything challenging during school time because of all the damage the school had done. DW bought some good behavior certificates, which DD had always valued receiving in public school, and told her to earn one, she'd have to make it through a whole school day without yelling. It took her a few weeks to earn her first one, and now she's getting them fairly regularly.
In either case, we make the goals measurable and achievable, and it seems to work for us. This differs from my own mom's approach, where the goals were unmeasurable and unachievable. My favorite was, "Until you start acting your age!" Wha...???
The other problem area is one you've already acknowledged: inconsistency. If he feels like the punishment isn't going to stick, then again, he's got no external reason to change his behavior.
It might help to discuss with your DH how the consequences he experiences for being inconsistent are more tiring than the alternative, because eventually, it means he has to get involved less, because the behavior improves. So if he's tired, that's all the more reason to back you up.
It also might help if you let your DS know that Dad is no excuse for violating the terms of any punishments you've given him, by taking away something else, too.
