Yes, well it's quite plausible that they have been hit with a tax bill from Germany, whether it be in respect of past earnings from patient treatment, or indeed something else.
But then the question would be; why don't they just get on and pay it, and be done with it?
They would surely do that if the amount was relatively small. By that I mean under about $40k. Once you get above about $50k, then you might be in the realms of disputed liability, a process which could drag on for yonks.
But is the tax issue actually the substantive reason for the non-appearance of the 10-Q? That remains to be seen...