The bank has concerns regarding the source of the funds of all their clients. They are subject to regulations by the country and, as you mentioned, this could vary depending on the country. If Bitcoin is not approved by the country, there is a high likelihood that the funds may be put on hold as the authorities have the power to do so.
I have made it very clear that all depends on the country and if the country is a cryptocurrency friendly or not. There was a time when Bitcoin was banned in my country, and as the op said the f you go the bank to lay a complain about the issue you were facing in the account and you be given a form to fill and in the form there was a a place or a column to fill that if you are involved in cryptocurrency or not and that was when Bitcoin was banned but now that column has nothing to do with the people again since Bitcoin has been unban in the country. But before then, nobody ticked that place but people ticket because bankers are looking for where to buy Bitcoin p2p in a cheaper rate.
Telling people that you are investing investing in cryptocurrency is not a bad thing because I see nothing wrong for that since cryptocurrency is not a criminal activity.