Nightly ifup breaks ipv6

Some time ago I had a problem whereas my Android phone would lose IPV6 connectivity after the ISP-mandated nightly disconnection of the DSL uplink. My workaround was to schedule "ifup" for both internal networks, "casa" (aka lan) and "guest". This apparently worked well with no side-effects on other devices.

Recently upgraded to 23.05.0 and then I had the problem that my desktop (wired) would not get an IPV6 address, rebooted the router and apparently it was ok... apparently because it happened again that I had to reboot in order to have IPV6 active after the nightly ifup, so I am beginning to think that this is NOT a coincidence.

For the moment I have disabled the "ifup" but I am curious: what is different from the router bridge interfaces being brought up during boot and being restarted later?

Is it possible that your clients are using a dynamic IPv6 prefix?
Dynamic IPv6 | Minimize prefix lifetime / deprecate old prefix on reboot / prevent prefix release - #90 by dave14305

Hmm, I don't think so: I have a static /48 from he.net and it is the ifup for casa / guest which is breaking client IPV6, not that of wan. (I am not 100% sure about this last part but tomorrow I'll know for sure)

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Yup, reconnecting wan (and he.net tunnel) without forcing my Android phone to reconnect (with "ifup casa" and "ifup guest") will make it lose IPV6 connectivity until I toggle the wifi off and on. Another Android device (mibox4) is unaffected, interestingly.

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I am going to try to restart only the wifi, if it makes any difference. I could also script a force-disconnect but in the end I'd still like to understand what is different between a reboot and a runtime change.

/sbin/wifi also fixes the IPV6 loss on my phone, for the time being I am sticking to that.
I guess I should check if hotplug extras is still working fine.