Weird link behaviour with RealURL

[sphkress]

When using YAG-Gallery with RealURL, links cannot be followed. As soon as RealURL is disabled, the extension works as expected. I googled all day long but didn't find a solution but instead a few unsolved issues.

This is the link without RealURL

localdomain/index.php?id=115&tx_yag_pi1%5Bc288%5D%5BgalleryUid%5D=1&tx_yag_pi1%5Baction%5D=index&tx_yag_pi1%5Bcontroller%5D=Gallery&cHash=286d3284c002815e915a6e6fcc783602
==> albums are shown, links working

This is the link with RealURL activated (and settings as recommended in realurl_conf.php!)

localdomain/galerie/?tx_yag_pi1%5Bc288%5D%5BgalleryUid%5D=1&tx_yag_pi1%5Baction%5D=index&tx_yag_pi1%5Bcontroller%5D=Gallery&cHash=286d3284c002815e915a6e6fcc783602
==> remains on gallery list page, links not being followed

PHP 7.0.9, TYPO3 7.6.15
YAG 4.2.1
pt_extlist 2.40
pt_extbase 2.3.0
RealURL 2.1.5