I think sololearn server becomes very hot due to lot of pressure .That's why sololearn takes a break in Sunday as it is the national holiday of USA😄😄.
You can email to [email protected] about this but give email with details including the country you are using in sololearn.
I do not experience this issue.
Could it be related to your network/ISP?
Sometimes, when using one of my data sims the site/app fails to load. Switching to a different network fixes the issue.
Try wifi, another service provider, etc. It may fix the issue.
In any event feel free to contact sololearn via settings, feedback to get more help/assistance and possible solution to your issue.