Thanks for the question.
There is no limit to the number of custom fields that can be added to a field group or in your case the repeater. Your server might be terminating the save process before ACF completes its job, you will need to increase the max_vars PHP setting. You can make the following changes to your php.ini file:
max_input_vars = 3000 suhosin.get.max_vars = 3000 suhosin.post.max_vars = 3000 suhosin.request.max_vars = 3000
The WSOD might also be as a result of a plugin conflict, please deactivate all other installed plugins and switch to one of the stock WP themes to check if the issue will still pop up.
To update the plugin you will need to log in as an admin.
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