After reviewing one of the reccomended acrobat posters advise, it didn't totally provide the answer, but got me close enought that I was able to fix the checkbox issue (of unchecking all the boxes when being sent for signature) and didn't have to use the old acrobat version.
It's in the signing phase that I had to check the boxes.
Initially, I completed all the fields on my PDF form as I normally would, except check boxes.
Then, I select 'E-Sign' > 'Requested e-signatures' > add email receipients.
I moved to the next step, 'Prepare document'. This is where you can edit form fields and assign to receipients. It's within this window that you'll notice if you double click on a checkbox, the left side window pane shows options to customize the check box field. The checkbox defaults to 'unchecked'. I had to update the 'Checkbox default' dropdown to 'Checked'. That maintained my check boxes, and unless the receipent changes it, they stay checked. Not crazy that you have to wait until you are sending the document to check the box, but it worked and I don't have to change back to an old version of acrobat!
This is the post that I referenced:
"In the meantime, you may try filling in the form field after you update it on Acrobat Sign. Use the Prefill option (https://helpx.adobe.com/sign/using/prefill-forms-field-before-sending.html) to input the information on form fields before sending it. "
I completed all the fields, except check boxes. Then, I 'requested signatures' and added receipients. I moved to the next step, 'preview', where you can edit form fields and assign to receipients. It's within this window that you'll notice if you click on a checkbox, the left pain will bring options and show the checkbox default to 'unchecked'. I had to update the checkbox default to 'checked'. That maintained my checkboxes and worked flawlessly. Not crazy that you have to wait until you are preview the document to check the box, but it worked and I don't have to change back to an old version of acrobat.
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