https://support.wix.com/en/article/supported-browsers#supported-browsers-for-mobile-devices
in terms of the official support assistance, Wix in general can assist our user’s with iPhone 7 and above, but we can not guarantee how older devices will behave
as for the Editor X built sites, the rule will be the same, but such behavior in terms of the lower breakpoint is not expected inside of the builder, since the Editor X supports devices from 320PX width resolution
can you share the sitelink you are working with, so we will be able to check how it is looking inside, possibly such layout is system issue