IPv6 issues in "best region" mode?

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Hi -

Like others using Photon PUN, I have had (and previously resolved) Apple App Store review issues before. Now there are issues again, I suspect because of IPv6 requirements. When using the "Best Region" mode in settings, I see that all of the regions are pinged, e.g. 92.223.82.17:5055 for US east. This suggests that it would not be compatible with an all-IPv6 situation...and thus related to the App rejection. So, is this Best Region mode, in fact, not compatible with IPv6? or is there likely a different issue? I'm using PUN v. 1.101 and Unity 2018.3.0f2.

Many thanks!