The topic is of interest in principle, since I basically run all peers on all my Synologys with “Ignore permissions” checked.
Why it works then is not finally clear to me either. However, it also seems to me that there are conflicts between the Windows ACLs and the Synology ACLs. This makes logical to activate the option.
Since the Web GUI can also be called up on the Smartphones, I have found that all peers created already by default with “Ignore permissions” checked, ie without intervention. It therefore seems to me that there should also be a decoupling between the ACL systems in the same way.