I was following today’s SFOS meeting for exactly this issue. The data connection problem is mainly discussed with respect to the Xperia 10 iii. However, the Xperia 10 ii is affected similarly.
If I am not mistaken, the connection problem only arrived at the Xperia 10 II with SFOS 4.4.0.68, the first release with VoLTE for the Xperia 10 ii. Therefore I wonder whether the connection problem with the Xperia 10 II/III with Telekom/Congstar DSIM is related to VoLTE support
Someone else had a similar suspicion, see this thread as also hinted to by @Fubo although @flypig said it was fixed " ** For issue 3, a fix was introduced to work around the fact that VoLTE can create new IPv6 interfaces with potentially broken routing data (this is carrier dependent). This fix was rolled out in Sailfish OS 4.4.0.68: (flypig, 07:22:35)* "