I have the UB Content Slider on Magento 2.4.1.
And there are 2 backend users with different Locale, EN_US and EN_AU.
However with user EN_US, I can save the slider item, but with EN_AU I cannot. (I believe the error comes from date-time validation).
Can you please double check from your site?
Could you please us know the version of UB Content Slider module in your instance?
Meanwhile, we noticed that your subscription has expired for a long time since July 2017. Please consider renewing the subscription to get access to the latest UB Content Slider package which is fully compatible with Magento 2.4.1.