Connection interrupted on a previously working account points at something that changed in the path between client and server, checked from the local side outward since that is where changes usually happen:

The local network first, the common cause: an unstable internet connection drops the mail connection mid operation, so check whether other online activity is also flaky, test on a different network to isolate and restart the router if the whole connection is unstable. A connection that works then interrupts often traces to intermittent local networking rather than the mail server, the first thing to rule out.

Security software, the frequent culprit on a previously working setup: antivirus and firewall email scanning can start interrupting connections after an update or a settings change, since these products proxy the mail connection and a broken proxy drops it. Temporarily disable the antivirus email or SSL scanning and test, and if it stabilizes, update or reconfigure the security software rather than leaving protection off, the antivirus mail component being a leading cause of newly appearing connection interruptions.

The server settings and status, next: confirm the incoming and outgoing server settings, ports and encryption still match the provider's current requirements, since providers occasionally change these and check whether the provider has an outage or has flagged your account, which presents as connection problems. A large mailbox or a specific stuck message can also stall a sync connection, worth checking if the interruption happens at a consistent point.

The isolation sequence: test on a different network to separate local networking from the account, disable security software temporarily to check its involvement, verify settings against the provider and check the provider's status, and try a different client or webmail, since webmail working while the client interrupts points at the client or its machine while both failing points at the network or account. Most previously working accounts that start interrupting resolve at the local network or the security software, the two things that change underneath a working setup and break the connection the client relies on.