You are most welcome!
The accidents and regression are a fairly common way that very young children express anxiety
/insecurity. However, sometimes these can point to a more serious issue.
I would suggest that you check in with Jack and find out if something is going on when he visits his Mom that is more than just the freak out about being away from home. Don't necessarily grill him and make him wary or nervous, but just ask how it is and find out what he does not like. Make sure that Mom doesn't have some creepy friend/babysitter/bf, for example, who might be causing him distress.
Also, check in to see if there is something happening to upset him at school or daycare or other situations that might also be a possible source of problems.
If there are still concerns, you can start with taking Jack to the pediatrician for an eval and advising. Don't hesitate to see a family therapist if things seem really askew, but I am hoping for you all that only minor adjustments are needed and that things will be better resolved for your family soon.
Best regards, Patience P.