Hi Mooz80 and welcome to the Lincoln Forums. If adjusting the volume while the system is reading a text does not help, and/or will not hold the desired volume setting:
The first step would be to schedule a service appointment with your Lincoln Service Department and physically demonstrate the problem to the Service Advisor. If the problem is still not corrected after this visit (or you have already done this), contact Lincoln Concierge and have a case opened.
Keep in mind that if they do not have an available solution, they will probably recommend scheduling another service appointment, either with your current dealership, or another Lincoln (or Ford Dealership, if you are not happy with yours). Just mentioning this so you are prepared and do not get frustrated.
By doing this, Lincoln/Ford will be made further aware that there is an issue, which is possibly inherently widespread.
I am sure others will also jump in to help, so keep us updated and good luck.