I am using EE v2.5.5 and Matrix v2.5.3.
In Matrix, I'm able to add up to 50 rows without problems. When I add more than 50 rows and click the Submit button, I am returned to the entry edit form again.
Is there a 50 row limit on Matrix fields?
You may already be aware of this, but you could try to switch over to Grid, the native built-in EE fieldtype. They do the same job with very little difference. And Grid might not have that 50 entry limit.