Yes, unfortunately, there does seem to be problems with the Server Check as reported by others https://dev.tiki.org/item6665--Server-Fitness-tiki-check-php-Never-Opens
There have been a lot of changes in Tiki 18.3, which seems to work ok with php 7.1
Maybe try that configuration to see if you have better results (this works fine for me, but Server-Check still does not).
Keep in mind, Tiki is very different from all other CMS's as basically all features are 'built-in' vs. a base CMS plus a million external plugins. This model is significantly more work to maintain, but inherently much better / secure / stable for business (no external reliance's). And, Tiki is basically an open source MS Office replacement, yet without the $$billions that MS has. That said, there is an amazing group of passionate developers very dedicated to constantly making it better.