It is normal for a site to have problems. Even the most experienced sites can still run into problems. What was the main problem in the beginning is that players have not been paid out or that there were other problems with paying players. That's the most important thing about a site. I think they underestimated the project, or hired too few software testers to thoroughly test the platform first.
In my opinion, what happened was not because they underestimated, but it was very possible that they didn't have a competent development team in their field so that the launch didn't go smoothly, moreover they didn't anticipate the abuse of bonuses so that everything looked so very chaotic. Wait for May 28, maybe there will be another delay but if this happens it's very unfortunate.
well this most likely happened to them during their initial run of casino since the OP is still hiring a competitive developer a few days ago after there announcement of the opening date. This is common for team that only built online since there's no physical interview to see the qualification skills properly on an online interview. The new website UI/UX is already improved drastically so I'm sure that the team is already aware about the things they need to fix before they open again the casino.