Today (November 21st 2018) saving to data base is not working, whether there is any issue’s with bubble.is server
No issues here…
Did you try doing the workflow step by step to see what is happening exactly? Did you look in the server log to check if anything happened? Are you checking the live database vs the dev database? 
In server log it says Bad regex format, I am using the regex format in find&replace (?<=^.{0}). to change the 0th position of a string, it works correctly with text field and input field and also in work flow I copying the changed value to database and viewing the value in different text box (value of that database filed) it shows the correct data. But When I looked in to the actual database it’s not changed.
Please held in the above regex format
Did you end up solving this? I think I am seeing something similar here: Regex produces errors only on safari