The important factor to remember is that ultimately US Customs agents are government employees. Meaning you will encounter a variety of competence and knowledge just as with any other government employees. I always come back from Cuba through Houston. Over the years I have found it all just boils down to luck oi the draw on the Customs agent you get, their knowledge and what mood they may be in.
Returning in 2020 I admitted to having two boxes of cigars in my carry on ( I had several hundred more in the checked bags that I didn't believe were part of the discussion). The agent asked me if I was allowed to have that many. When I said yes, he asked a coworker that said "he can have as many as he wants. The Cuban embargo is over." I wanted to ask for his name and schedule so I could go through his line every time, but discretion told me to just shut up and accept my good luck.
In 2022 the Agent asked me where I was coming from. When I said Cuba his entire demeanor changed and he asked me if I knew that Cuba was on the list of State sponsors of terrorism. He wasn't interested in hearing that Americans are allowed to travel there under 12 catagories as outlined by the US State Department. Without any further questions he turned to his computer and began typing like he was in a FB argument. What seemed like an hour later (probably 2 minutes) he hollered out for an escort officer. I was told to fetch my checked bags and they were thoroughly searched. Every single cigar was found and the searching agent walked off suddenly and wordlessly leaving me standing alone wondering what the hell was going on. When he returned from a side office he said "I'm going to use officers discretion and allow you to keep your cigars. You can put them back in your bags." I never walked so fast in all my life as I did heading for the exit that night.
In 2023 the couple in front of me said they had nothing to declare and the agent asked them why they didn't bring anything back. They said they were told if they brought anything back it would be confiscated. The agent assured them that wasn't true and they could have brought back rum and cigars. I chose to remain silent and didn't admit to having anything to declare. I flew through without any issue.
In February of 2024 the guy in front of me got the "I need an escort officer" treatment and was taken off for additional scrutiny. When the agent called me forward I said "I need to know exactly what that guy said to you so I don't end up like him." The officer broke down in laughter and the only question I got was where was I coming from mixed in among the laughter and a closing "get the hell outta here."
There you have it four different officers and not one of them knew the actual laws they are tasked with enforcing regarding Cuban goods. At the end of day it just comes down to pure dumb arse luck and maybe a bit of how serious the agent you end up in front views their responsibilties. And those are just the last four trips. The ones before those were a wild grab bag of agents that were just as bewildered.