Wordpress - The Events Calendar Pro & Event Tickets Plus Changes

Hi,

We're a small company and are working on a website with several plugins of Modern Tribe Inc. We have one big issue "The Events Calendar" has an input problem. It works fine with 10 dates, but adding more (we need over 400) it doesn't really work anymore. We would only need text fields for date/time nothing more. But the plugin works with a calendar (as seein on the image) that part of code is loaded like with each date... that clearly is not working well.

We had another developer fixed it, it costed a lot, out of principe we want to finish the site, but we lost all of it. The problem is ... after an update the changes were all lost AND the developer didn't knew what he changed... So all is lost... Eventually the developer completely dissappeared...

I hope that there is someone being able to help us out here. There is a demo available to check some things.

Thanks in advance,
Michiel

P.S. We will pause the project to contact the people who did an proposal.