When Revolut first launched in Singapore, it was almost common knowledge that depositing more than $5,000 SGD (approximately $3,500 USD) would more or less cause one's account to be limited for weeks (until one tweets at them to hurry up), because they've triggered the Source of Funds check.

Did you do anything "weird" or was it just during your average months that they suddenly went ballistic?

I know they're supposed to alert the authorities on suspicious activity, but I believe(d) freezing an account unilaterally is the ultima ratio for extreme cases and wouldn't be done easily, as it will leave the bank open for damages claims, and really makes banks somewhat useless if it happens frequently.