image count issue/limit?

Hi there,
thank you for this module, using that on every site :)

In past I had no problems to upload 200 - 300 images.

Nowdays when I load say 300 images, all is on server temp, form for creation of content is creating thumbs, but only for half, ending with file #165, other files are wthout thumb image, but at least stated somehow that are "there".
When I tried to save, its strangely saying drupal error that some other mandatory field xy is not entered. field xy was entered and there is no conditional connection to image filed, only that in form it comes directly after image filed.
I tired to lower the file sizes, to see if max count will be higher, but still 165.
If I upload say 160 it works.

as it worked before, I am wondering....
Maybe recent update of drupal core ruined that?
Or update of server/php, but I think php limits are pretty the same....but of course possible.
Can you please guide me or suggest?

tried dev and latest prod.
Thank you