If your data roaming is not working properly in Italy, it might be the IP protocol

I'm using mobile data roaming all over the EU, but when I come to Italy, most apps and Internet sites stop working. I can use some messaging services and access google.com, but that's about it. I have the APN protocol set to IPv4/IPv6 by default. I changed the APN protocol and APN roaming protocol (from the Access Point Names setting on Android) to IPv4 and was able to access all sites normally after that.