Hi @edusz,
Thanks for reaching out. From inspecting your site manually and using the tagassistant.google.com service I can see there is a Google Analytics 4 (GA4) snippet placed n your site via Site Kit, which is tracking visits at present.
As you don’t have a Universal Type Analytics (UA) snippet placed on your site it’s normal that the Site Kit dashboard won’t display any data, as this dashboard at present displays information based on a UA type snippet only and not a GA4 type snippet. This will change in the future, as more users migrate to GA4 and the GA4 API allows for the same features within Site Kit at present.
In your case, regarding the missing data, is it possible that you, or another administrator, may have removed the option for Site Kit to insert a UA type snippet on your site, around the timeframe you mentioned (May 19th)?
What you can do, to ensure you can view current traffic within the Site Kit dashboards, is to allow Site Kit to insert a Universal Type snippet also, along with the GA4 snippet that’s currently inserted (Site Kit > Settings > Analytics > Edit).

Unfortunately if you didn’t have a UA snippet tracking from May 19th there won’t be any data from that date until the time you activate the UA snippet however it will display data from the time you allow Site Kit to insert a UA snippet.
Let me know if you have any questions with the above.