Lindyrig79, Tho I will be of no help to your existing issue unless you decide to rout out the existing grout and regrout. But if you do,,, Bostick (and others as well) makes a grout product that I learned about building national chain restaurants. It is the closest thing to using the nasty epoxy grouts that maybe required in their kitchens. Urethane grout has been my answer so far. I’ve only been involved in using this for 15 ish years so far and I try to keep in touch with customers with is and do visual inspections within the 1st, 3rd and 5th years after the install. I have this in my own home on 2 different installs.
The grout is color true to color throughout and has matching caulk in smooth and sanded tubes. Easily 15 to 25 colors I don’t remember. Remember as always it is the PREP of the install that is THE most important part! Complete WATERPROOFing, backing for accessories and complete attention to detail is to be of the utmost importance.
https://www.bostik.com/us/Bostik-products/trucolor-rapidcure-pre-mixed-urethane-grout
I am a true believer. period!