Suddenly no streaming video anymore from settopbox

[harrieb]

About a week ago I installed OPNsense with Zenarmor (Home) on a Topton mini pc.
Everthing worked fine untill a problem occurred with a wired TV settopbox
At first the image freezed and later the images where played at high speed.
Then the STB gave a warning that there was no internet. It still does.
The STB received an IP adress and a connectivitytest on the STB showed no issues.
(I have little network knowledge and just started with OPNsense)

Connecting the STB with the ISP modem works fine.

Versions:

• OPNsense 25.1.5_4-amd64
• FreeBSD 14.2-RELEASE-p2
• OpenSSL 3.0.

Topton mini PC:

• Celeron J4125 CPU with 8 MB memory, 40% in use.
• Is behind the ISP router in bridge mode
• Three ports in use:

             Igc0, cable from ISP modem (IN)
             Igc1, cable to switch (OUT), which is connected with STB
             Igc3, cable to ISP modem for login


I have tried:

• Reset STB,  switch, ISP modem, Topton mini pc.
• Changed UTP cable from STB to wallmount.
• Connected STB with other switch.
• Other STB (upstairs) shows the same issue.
• Packets captured imported in Whireshark. See Attach_1 and Attach_2 (I am unfamiliar with Whireshark)
• OPNsense and Zenarmor logfiles viewed. No blocked hosts (Dynamic DNS)
• Removed  Topton mini pc igc3 cable
• STB ping from Topton:

             55 packets transmitted, 55 packets received, 0.0% packet loss
             round-trip min/avg/max/stddev = 0.856/1.014/1.823/0.121 ms


Does anyone have an idea ?