subdomains crashed

[DragonZX]

I am using two domains in my ispcp - domain1.com and domain2.com
then I has created users on a 3-rd level domains
sub1.domain1.com
sub2.domain1.com
...
sub1.domain2.com
etc

For three month it was working normally, but now
sub1.domain1.com Aliasing to domain1.com and other subdomains
sub1.domain2.com is working normally

What I must do to fix this problem?