Adding a bit to what mrsD wrote:

The MV transporter can only transport one of its substrates (iodide, biotin, lipoate and pantothenate) at a time. It can not transport any two of them (eg, biotin and lipoate) at the same time.

What this means is that all of its substrates are what are called competitive inhibitors of each other. This means that relatively high concentrations of any of its other substrates will inhibit transport of biotin.

So, as mrsD suggested, discontinuing lipoate for a while is worth a try to see if you notice any improvements. That way lipoate is less likely to act as a competitive inhibitor of biotin transport.