It looks like there were a few 504 errors on the domain stimulance.co between 2026-04-22 15:17:50 and 2026-04-22 16:31:18. I checked the load for Johnny during that range and it was between 9.32 and 16.14 so pretty normal and not too bad. 504 errors like this on PHP can happen due to quite a few things such as DDoS, zombie PHP processes, or just too many people trying to use PHP at the same time. Generally an Apache restart clears it up or if it's a DDoS it clears itself once the attacking IPs are blocked or stop attacking. It also kind of depends on your software. Some PHP software like Wordpress is extremely bloated and normal page loads take 5-10 seconds on Johnny anyways. If your PHP software is super slow on a good day, then it's even more likely to show a 504 error when the server is busy. Highly optimized fast PHP sites that normally only take 100 milliseconds to load a page on a good day may slow down to 5 seconds per page load when the server is busy, but won't show a 504 error.
Wolstech already said it, but the best option is to upgrade to Morty https://heliohost.org/dashboard/move/ if you want better uptime. Our mission as a non-profit is to provide free hosting to as many people as possible so the free plan is kind of overloaded by design. Our mission isn't to provide 100% uptime, super-fast, free hosting to only 10 people, so as long as the uptime is above 97% we consider it "good enough" for a free plan and load as many more free users as we can on there.