Strange speeds on shedule

[PrzemekSkw]

Hello, I don't want to make bug report. Just looking for explanation for my situation.
When my ISP give me new fiber connection 600/600 I buy two reapeters and connect to my TP-Link router (that give me easy-mesh solution). I have router in my bedroom and two reapeters in living room. To one reapeter I connect firecube with Ethernet cable and to second reapeter I connect unRAID server (also Ethernet cable).
I have speedtest-tracker installed on unRAID as docker. All month when they connect me that fiber internet speeds was like on screenshot:

Last few days something strange happen.
Speeds tracking are much slower.

When I set manual test on speedtest-tracker I get about 600/600.
When I test with wifi on smartphone also 600/600.
I reboot server, I reset two reapeters and router but still the same situation.
Meybe somebody can explain what happen?
Regards.