It would appear the Judge exercised some errors in judgement. Everyone has their own opinion about whether they were intentional or not.
I can point to two things off the top. First, the Judge let Stormy Daniels go on and on disparaging Trump and divulging sexual details. This seems a bit odd when you consider her testimony doesn't really add a whole lot other than to give her a sounding board for her personal dislike of Trump. You don't have to believe my take. The Judge basically told the jury to ignore certain of parts of her testimony. This kind of sets up a self-evident appeal.
Lastly, the Judge wouldn't allow the defense's Federal campaign finance law expert testify. If you follow the dots that many have obfuscated, the case actually hinges on the question of a campaign finance violation. The Judge also let Cohen liberally comment on Federal campaign finance law which further complicates things for an appeals court.
The Daniels testimony was spicy. But he didn't allow it. If you understand what happened, she went off the rails when questioned. He specifically told the defence that it was their job to object to this type of thing....which they didn't. Trump's team wanted a mistrial. He denied it. It is doubtful this would be worthy of appeal.
As for the witness, there is a long-standing precedent about expert witnesses. Basically, they are not allowed to interpret the law, which is what the defence wanted. And, the prosecution already had an expert witness, so the defence could have used him to prove their point. But they didn't. And, there was a legit concern that bringing in another so-called expert would just confuse the jury. That is probably what Trump's team wanted, but 99% of judges (with the exception of maybe Aileen Cannon) would not allow.
Now, as I have mentioned in a previous post, I am not a lawyer. But from the credible news sources covering the trial, there isn't a lot of concern about the appeal. But, again, that also depends on a conviction, which is never an assured thing.