Challenges with gform_pre_submission / gform_pre_submission_filter

I had been previously using gform_validation and at the conclusion of all validations doing the form modifications needed. Saw in the documentation that Gform_pre_submission or Gform_pre_submission_filter would be better place for that kind of work. Trying to do so lead to two rather strange issues.

If I use Gform_pre_submission_filter following the basic examples in the documentation, upon submission of my form instead of success message I receive a page not found with the URL having an extra /:/ at the end.

If I use Gform_pre_submission following the basic examples in the documentation, I can't get it to do any actual updates. The code below is a small subset example.

add_filter("gform_pre_submission", "pre_rideshareSubmission");

function pre_rideshareSubmission($form){

	$_POST["input_6"] = $_POST["input_13"] . " TO " . $_POST["input_28"] . " ON " .  $_POST["input_10"];

	}

This thread was the closest I could find that relates.

I have the same issue when using this filter, it adds that strange /:/ string at the url, the form stops saving the post to database and instead of sucess message, it points to a 404 error page.

Man. How did you get to solve this?