HELP - Only last 8 e-mails are shown, rest is gone?!

HELP - Only last 8 e-mails are shown, rest is gone?!

So for years I used Zoho Mail without problems, but now the 2nd problem in 2 days, and this one is huge:

All my e-mails are gone except the last 8, see picture (german version of zoho-mail). Even though it says correctly that there should be 7315 e-mails in the inbox (german: "Posteingang"). Please help me getting my e-mails back asap!