Some German trains were notorious for having bad cell signal due to metal-coated windows (applied for reflecting solar radiation). It's the first thing I thoug

Some German trains were notorious for having bad cell signal due to metal-coated windows (applied for reflecting solar radiation). It's the first thing I thought of, and it's why we had ceramic tinting put on our vehicle windows instead of conventional tinting (which in many cases, AIUI, has radio-blocking metal in it).