Redirect to principal domain

hy serge,
sorry for the late reply ??

we are aware that sometimes redirections occur, where we could not find a good solution to find out the cause easily. i would suggest that you try our partner plugin, which is described here: https://www.falkemedia.at/multiple-domain-mapping-on-single-site-premium/

i hope this will work for you. unfortunately we cannot provide deeper support since lack of ressources for our free plugin by now ??

good luck,
matt