My CMS form is unreliable. Can I do anything?

Question:
I have a cms form on my site that was completed by 60 users already. Approximately 10% of the submissions in the data collection are incomplete (eg missing names and emails), although the missing values are mandatory. Apparently, not all data is transferred correctly. Could this be due to the fact that an image upload is also mandatory, which then causes a time-out with larger files and disrupts the transfer. Are there any workarounds? Many thanks for your help!

Edit: Found out that many users whose data didn’t go through used the Safari browser.