Thanks for your patience, I guess I never thought of the Synology NAS being the culprit. But you are definitely unto something. At first I tried to get into back the scenario of sub 100Mbps network speeds. Once again playing back several demanding videos helped. This is the iperf3 to the NAS (not the same switch btw):
Connecting to host 192.168.0.199, port 5201
Reverse mode, remote host 192.168.0.199 is sending
[ 4] local 192.168.0.49 port 43532 connected to 192.168.0.199 port 5201
[ ID] Interval Transfer Bandwidth
[ 4] 0.00-1.00 sec 16.6 MBytes 139 Mbits/sec
[ 4] 1.00-2.00 sec 9.34 MBytes 78.4 Mbits/sec
[ 4] 2.00-3.00 sec 9.72 MBytes 81.6 Mbits/sec
[ 4] 3.00-4.00 sec 1.80 MBytes 15.1 Mbits/sec
[ 4] 4.00-5.00 sec 3.91 MBytes 32.8 Mbits/sec
[ 4] 5.00-6.00 sec 6.20 MBytes 52.0 Mbits/sec
[ 4] 6.00-7.00 sec 8.26 MBytes 69.3 Mbits/sec
[ 4] 7.00-8.00 sec 3.45 MBytes 28.9 Mbits/sec
[ 4] 8.00-9.00 sec 1.03 MBytes 8.63 Mbits/sec
[ 4] 9.00-10.00 sec 4.21 MBytes 35.3 Mbits/sec
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval Transfer Bandwidth Retr
[ 4] 0.00-10.00 sec 64.6 MBytes 54.2 Mbits/sec 33 sender
[ 4] 0.00-10.00 sec 64.5 MBytes 54.1 Mbits/sec receiver
To the laptop (same switch):
Connecting to host 192.168.0.104, port 5201
Reverse mode, remote host 192.168.0.104 is sending
[ 4] local 192.168.0.49 port 38358 connected to 192.168.0.104 port 5201
[ ID] Interval Transfer Bandwidth
[ 4] 0.00-1.00 sec 109 MBytes 918 Mbits/sec
[ 4] 1.00-2.00 sec 111 MBytes 934 Mbits/sec
[ 4] 2.00-3.00 sec 111 MBytes 934 Mbits/sec
[ 4] 3.00-4.00 sec 110 MBytes 926 Mbits/sec
[ 4] 4.00-5.00 sec 111 MBytes 935 Mbits/sec
[ 4] 5.00-6.00 sec 111 MBytes 934 Mbits/sec
[ 4] 6.00-7.00 sec 111 MBytes 935 Mbits/sec
[ 4] 7.00-8.00 sec 111 MBytes 934 Mbits/sec
[ 4] 8.00-9.00 sec 111 MBytes 934 Mbits/sec
[ 4] 9.00-10.00 sec 111 MBytes 934 Mbits/sec
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval Transfer Bandwidth Retr
[ 4] 0.00-10.00 sec 1.09 GBytes 935 Mbits/sec 0 sender
[ 4] 0.00-10.00 sec 1.09 GBytes 932 Mbits/sec receiver
Interface to 100Mbps to the NAS:
Connecting to host 192.168.0.199, port 5201
Reverse mode, remote host 192.168.0.199 is sending
[ 4] local 192.168.0.49 port 43534 connected to 192.168.0.199 port 5201
[ ID] Interval Transfer Bandwidth
[ 4] 0.00-1.00 sec 5.55 MBytes 46.5 Mbits/sec
[ 4] 1.00-2.00 sec 5.31 MBytes 44.5 Mbits/sec
[ 4] 2.00-3.00 sec 5.57 MBytes 46.7 Mbits/sec
[ 4] 3.00-4.00 sec 5.52 MBytes 46.3 Mbits/sec
[ 4] 4.00-5.00 sec 5.45 MBytes 45.7 Mbits/sec
[ 4] 5.00-6.00 sec 5.51 MBytes 46.2 Mbits/sec
[ 4] 6.00-7.00 sec 5.64 MBytes 47.3 Mbits/sec
[ 4] 7.00-8.00 sec 5.20 MBytes 43.6 Mbits/sec
[ 4] 8.00-9.00 sec 5.08 MBytes 42.6 Mbits/sec
[ 4] 9.00-10.00 sec 5.20 MBytes 43.6 Mbits/sec
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval Transfer Bandwidth Retr
[ 4] 0.00-10.00 sec 54.1 MBytes 45.4 Mbits/sec 2232 sender
[ 4] 0.00-10.00 sec 54.0 MBytes 45.3 Mbits/sec receiver
Interface to 100 Mbs to the laptop:
Connecting to host 192.168.0.104, port 5201
Reverse mode, remote host 192.168.0.104 is sending
[ 4] local 192.168.0.49 port 38406 connected to 192.168.0.104 port 5201
[ ID] Interval Transfer Bandwidth
[ 4] 0.00-1.00 sec 5.44 MBytes 45.7 Mbits/sec
[ 4] 1.00-2.00 sec 6.63 MBytes 55.6 Mbits/sec
[ 4] 2.00-3.00 sec 6.79 MBytes 57.0 Mbits/sec
[ 4] 3.00-4.00 sec 6.72 MBytes 56.3 Mbits/sec
[ 4] 4.00-5.00 sec 6.47 MBytes 54.3 Mbits/sec
[ 4] 5.00-6.00 sec 6.74 MBytes 56.5 Mbits/sec
[ 4] 6.00-7.00 sec 6.77 MBytes 56.8 Mbits/sec
[ 4] 7.00-8.00 sec 6.98 MBytes 58.5 Mbits/sec
[ 4] 8.00-9.00 sec 6.41 MBytes 53.8 Mbits/sec
[ 4] 9.00-10.00 sec 6.78 MBytes 56.9 Mbits/sec
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval Transfer Bandwidth Retr
[ 4] 0.00-10.00 sec 65.8 MBytes 55.2 Mbits/sec 3369 sender
[ 4] 0.00-10.00 sec 65.7 MBytes 55.1 Mbits/sec receiver
Hope this points somewhere, once again thanks for your help.