An account been flagged for suspicion is not the reason why the OP account was locked cause this has been happening since the year 2016 when I have the same issue, I was lucky they unlock it after 2years but I have to submit my passport before they do so.
Coinbase is not a good choice for a non-US user.
I was under the impression they were one of the most trustworthy exchanges. From reading online the number of complaints regarding people having a similar experience apparently I was wrong.
They look shady as hell from reading this!
https://mashable.com/article/sec-coinbase-complaints-fraud