vodafone vs. telekom (both germany) - IPv6

[Thomas Schäfer]

Hi,

in the meantime I can compare the IPv4/IPv6 behavior of telekom (alias 
DTAG, t-mobile germany) and vodafone germany.
Telekom provides IPv6 (dualstack) at production level since summer of 
2015 and vodafone since last month.

With android smartphones both works.
But with ~50% of my surfsticks and modems ( I did not test the 
lte-routers yet, they don't need the ModemManager anyway) it doesn't work.

Anybody a clue what could be the reason?
Are there hidden flags, 3gpp-release/versions limits? Blacklists?

Some good cases are listed here.
https://www.thomas--schaefer.de/vodafone/index.html

The age seems to have no impact, the E398 is quite old.

Regards,
Thomas