My name is***** am another expert on the forum.
I am very sorry to learn of this situation.
Your son has 2 separate issues that you have identified in your post.
(1) He has an appearance date for next month. This is his responsibility to appear at, the reason he must appear is because while his attorney may currently have a report saying that he is incompetent to stand trial, this report is only evidence that a psychiatrist or other mental health expert believes he is incompetent - the Prosecutor's office is entitled to oppose this, and the court must rule on the issue.
Even if found incompetent to stand trial, that does not mean that the charges are automatically dismissed. That simply means that the court may impose a different sentence (such as committing your son to a psychiatric facility). Based only on the very brief set of facts as you have presented them, it is possible that the prosecutor's office will decline to press charges on the issue based on a finding of incompetence, but this is an issue of prosecutorial discretion, it is not a right.
But currently your son has an active case against him, he must appear.
(2) I believe there may be a misunderstanding between the attorney and yourself regarding obligations here - the attorney may have said it was your responsibility to ensure he shows up - but in reality it is only your son's obligation to show up. The attorney does not have a duty or obligation to ensure that his client appears in court, but if you wish to try to track him down, you can do so. If your son misses his court date again, the court may issue a warrant for his arrest and he will be subject to arrest and detention. pending a further hearing. (So even if he is found incompetent to stand trial on this issue and the DA decides to drop these charges, the court can still impose charges for the failure to appear).