Over the years, Wix has had a reputation of not doing too well with SEO and search rankings. Wix is a popular web site publishing platform and to have a bad reputation around SEO and search, that can be hurtful for adoption to it's platform.
Back in 2015 it had an issue with pages dropping out of Google's index and then most recently, to improve their reputation - they started a SEO Hero challenge which has been getting a lot of traction.
Last week, John Mueller of Google responded in a Google Webmaster Help thread about Wix and search and he said it "works fine." John said, "WIX websites work fine in search."
Here is his full message:
WIX websites work fine in search. There are a lot of different setups for new websites. I wouldn't focus too much on a single provider, but rather think about the bigger picture: which will make it easiest for you to maintain your site (adding / changing content)? If you're getting help from others for your site, is there one that they have experience in, which might make it easier / cheaper? Which one offers the features that you think you'll need in the mid-term? There are probably a few options that could work for you, so maybe it makes sense to just try some of them out and see which one works best for you -- websites are websites for Google :).
So another vote of confidence for WIX.
Forum discussion at Google Webmaster Help.