Node.JS developer who can troubleshoot

We are a small nonprofit that works with homeless in NYC.A board member brought in a developer in 2018 to develop a website for MR. Main component is a calendar where churches.schools, synagogues sign up for dates to volunteer. They get instruction on where to go, homeless people get info on where groups will be, etc. The developer is no longer around, and a friend/volunteer has been handling website maintenance (security certificates, small changes, etc). This weekend he made a small text modification on a page (changing officers on board), but when he went to push online, it wouldn’t come on. He spent a lot of time updating OS etc, now doesn’t get errors, but “The deployment procedure now completes without fatal errors, and the site is *almost* there (blank page instead of the Under Construction page). And when I look at the page source, it's the actual web site, it's just not rendering in the browser for some reason.”
So he says was we need is a Node.JS developer who can troubleshoot and fix whatever is preventing the site from working properly.The site runs on NodeJS 8 and MySQL, and is hosted ona DigitalOcean droplet running Ubuntu.

Not looking for a volunteer, happy to pay someone for what I assume is several hours work. Besides current troubleshooting, if the person was interested in being on a small monthly retainer, I’d be happy to do that , but at moment just trying to put out a fire