Question about D-Link Dgs-105

Hello everyone, I use this switch (D-Link DGS-105 5Ports) together with the UPC Gigabox and the Lindy network cables (S/FTP, Cat. 6, 300cm) cables, for about 2 months I have been experiencing lag spikes in Overwatch, so it is no longer playable. The question now can it be due to the switch? With a direct connection to the Gigabox (approx. 15m Cat5 cable), I could not detect any problems. However, there is still a 100% packet loss with Blizzard Looking Glass. Already done: Uninstalled antivirus. Restarted the Gigabox. UPC technician reset the distributor in the house (too much signal). NAS, UPCTV removed from the network. DNS new with : echo off Echo release ipconfig /release timeout -t 5 Echo Renew ipconfig /renew timeout -t 5 Echo Flush DNS ipconfig /flushdns timeout -t 5 exit Test with direct connection to Gigabox approx + - 60 minutes = no lags As soon as connected again via home network (Gigabox -> wall socket -> distributor in security box -> switch -> distributor in security box -> wall socket -> PC) I had lags of up to 4 seconds again. . The cable lengths I used (3m + 0.3m + 0.3m + 15m) through the wall wall we have another 10-15m of cable. I am at the end with my know-how... Switch defective? Thanks for your help