node-feedsub not fetching new items for several feeds

On a Raspberry Pi, I run a Node.js script that uses multiple node-feedsub instances, to fetch new items for several RSS feeds (every hour).

This is how I create instances for every RSS feed:

```
... = new FeedSub(url, { interval: 60, maxHistory: 999, autoStart: true, emitOnStart: true })
```

For each feed, node-feedsub fetches all current articles, when I start the Node.js script. For some, it will also fetch updates every hour. For others, it does not fetch any updates (it reports 0 new items every hour, but there are new items - checked by looking at the affected RSS feeds manually). If I then restart the script, it will fetch all the missing articles at start, but again no updates after that.

Example of an affected feed: https://seths.blog/rss

What can I be doing wrong?

(Is there a limit to the number of instances, since some work and others don't?)