When switching to HTTPS there is the possibility that you will lose your social share counts on Facebook. This can happen immediately after switching or sometime after.
Our tech team have worked hard to implement a workaround to ensure that any existing Facebook likes remain. However, due to a bug in Facebook itself, these can occasionally disappear.
So, if you should have them but don't see them, you will need to debug the URL via Facebook's tool and click the 'Scrape Again' button.
It's a straight forward process that you can find instructions to here: https://promotemyplace.zendesk.com/hc/en-us/articles/216230543-How-to-clear-the-cache-on-Facebook