Not strictly true. And the screenshots shown are of BasicUI using the built in charts. See https://www.openhab.org/docs/configuration/sitemaps.html#element-type-chart.
@aarefiev, that is very unusual behavior. Sadly I’m not sure which repo hosts the charting servlet. I’m going to guess core. All I can recommend is to look at the settings under Configuration → System → Regional Settings and make sure they are reasonable and if so file an issue. See How to file an Issue.