Luckily not but the "Th" sound particularly in "Thank you" has been pretty hard for me the last several years. Seems to slowly fluctuate which sounds give me trouble. So many times, literally uncountable, I've ended a conversation with "Th...th...th..th....I'm trying to say I appreciate it" or I can only say "Thank you" after the right moment has passed, such as after getting my stuff from a cashier and once I take a step or two away. Funny how it works but that one frustrates me as I like to be polite.