Timeline of events:

Woodward is a lawyer hired by the Trump PAC to represent Trump's co-defendants, including Nauta, and Tavares. De Oliveira is represented by another lawyer, Irving, also hired by the Trump PAC.

Tavares changed lawyers to one that is not funded by the Trump PAC, and has changed his testimony.

Prosecution files paperwork citing concerns about Woodward's ability to cross examine Tavares or call his credibility into question during closing arguments. At that time, the prosecution did not request a hearing because it wasn't clear that Tavares would be a witness yet.

Side note, lawyers are required to maintain privilege even after they are fired. Woodward may have privileged information about Tavares that would create an ethical conflict, like for instance if Tavares told Woodward something in confidence and then lied about it on the stand, Woodward would be in a quandry. He cannot challenge the testimony without breaching his responsibility to his former client, and he cannot give a closing argument where he says "That guy's a liar, and I would know because I was his lawyer."

So this was a known, expected issue.

During this hearing, the prosecution announced that they intend to call Tavares as a witness, and requested the separate hearing.

Woodward played dumb, saying he hadn't prepared to argue this point, and how shocked and appalled he was that such a thing could even be questioned. This despite the fact that there was already a previous hearing for Irving, who represented three other witnesses and will have one of his associates do thise cross examinations.

The judge, deeply in the bag for Trump, played along with the farce. However, she will be required to hold the hearing, and will likely need to rule that Woodward cannot cross examine Tavares or attack his testimony in closing arguments. Anything less, and it will be a layup appeal for either side. The prosecution could argue that Woodward was utilizing privileged information, and the defendant could argue that he did not get a proper defense because his lawyer had competing interests.

So while we can predict the outcome, it's also likely that she will use this as another reason to stall the trial and pretend she isn't trying to drag it out and give Trump a chance to be elected before he gets convicted. The judge admonishing the prosecution is just a little cherry on the shit sundae that is this trial. The concerns were raised previously, and the cited caselaw is "ibid." The judge was looking for a reason to justify an attack on the prosecution.