No connection to internet

I am trying to setup konnected alarm panel (v1 - nodeMCU). The panel won't connect to internet when I try to sync zones via konnected cloud. All the other devices connect to the same wifi without problems.

I tried to connect the same device via another connection (hotspot created form mobile network of same ISP) and it connects without problems. DNS were a first suspect but through I managed to find out that with mobile or landline (GPON) internet the ISP's DNS are the same. ISP further changed my DNS to Google's but still unsuccessful. 

I am attaching a log from unsuccessful connection via local network and successful via mobile network (hotspot creation). Important and not highlighted is the step "Time sync failed". This step takes a while to show (I don't know what is happening behind it). I first thought that NTP is problems but after changing those to Samsung's,  Google's etc nothing changes. I also tried port forwarding to no avail. As said no other device is having any problems. 

My konnected worked fine until I upgraded fw from v2 to v3. But this is not the reason since my problem lies somewhere in routing (mobile connection works and local doesn't). When upgraded the konnceted got new local IP but even if I make it static (to match the previous) that doesn't help. It could be something with DHCP leases (but those have 24h expiry and nothing seems strange). My ISP doesn't find anything strange with my connection or in settings of modem/router (one device). Any ideas what it could be? I am running out of them.