(since you are not using Fabric, I’ll move this over to the REST API section).
Does this consistently occur for a specific user ID?
Is there any reason why those spammy Tweets could be appearing in the timeline? i.e. are they being retweeted by someone the user follows, does the user follow the account(s) from which the spammy Tweets are generated?
If you are using the timelines methods in twitter4j then they should just be hitting the timeline methods on the public API, and I’m not aware of issues with those at the moment.