The planned tough Brexit makes wrinkles of Coinbase's management. In the past few days, the Stock Exchange has sent an email to all its EU resident members stating that they are preparing to move from the UK to another country within the European Union, so that it is still possible to trade cryptocurrencies for the fiat Euro currency without any problems. In the future, all foreign companies that have their subsidiaries in the UK will have similar problems. Brexit will not touch the cryptocurrencies themselves. The problem would arise when you want to trade bitcoin for Euro.
Your Exchange user email states that they will be informed of the next steps in a timely manner. There is no need to panic, because Coinbase will solve this little problem.