Managed to enable IPv6 which mitigates the problem. Some sites are now much more responsive. If it's related to latest firmware, would be interesting to downgrade and test again. Might try it later.

Recently bought pair of new BE65 Decos. Problem is that they are blocking access to some random sites. Mesh is connected to "Huawei CPE PRO 2" 5G mobile router in bridge mode. Internet speed...