The indicator is displayed when updates are available for the WordPress core, the plugins, the theme or language files. The latter in particular will probably apply to you. Language files are often installed automatically. This means that you can see that there are updates because there is an update for the language files, you click on Updates and it is installed and you can no longer see the output.
If you have plugin and theme updates installed automatically, this can also be a reason. The moment you click on updates or plugins, they have already been installed in the background.
Look, I mean, literally every time I log into my admin area there is an update indicated. The chances of that being a real, actual update EVERY time is pretty slim. I am talking about the fact I log in maybe 3-4 times a day. So, you are saying there is a language update available 3-4 times aa day, every day?
Whether and how often updates are available also depends on the number of plugins you use. I have over 200 plugins in a development system, where there is almost always an update available – either for plugins or for translations. This is of course a heavy example, but I think it illustrates the probabilities. In a normal production system, there tend to be fewer plugins.
If you are still unsure about this, you can also check for yourself whether and what has been updated. Take a look at the files in /wp-content/languages/ and /wp-content/plugins/ via FTP to see when they were last changed. This way you can see what has been updated. There are also plugins that help you to keep an overview and take over the update control for you. See: https://wordpress.org/plugins/tags/update-control/
Last update for languages according to FTP was in January. Plugins had an update yesterday, but the indicator is still there this morning, but not indicating in plugin.
Then this is related to some plugin of yours. If you see the indicator again, deactivate all plugins as a test. Is it gone then? Then one of these was to blame.
Also have a look under Tools > Site Health to see if any anomalies are mentioned there.
