Please help us help you and fill where relevant:
LimeSurvey version: 6.3.1 or 6.6.6 both
Own server or LimeSurvey Cloud: own
Survey theme/template: own based on skelvanilla
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Hi everyone,
hope you are doing well this time of year.

Once again I am here seemingly having tried "everything" and coming up emtpy handed. I am not a newbie at filling values with url params in LimeSurvey. Let me paint a picture:
I have two surveys, lets call them s1 and s2.
Starting of in s1 the participant is sent to s2 with url params -> works as intended..great!
From s2 the participant is now sent back to s1 (to where they left off) with url params, I can also see in the url that they exist and the right values are given, BUT -> values are not being saved to DB.

The variables s1 to be filled are not equation question in the beginning of the survey (so the participant passed them already) but hidden (not by css) , but that is also the case for the prefilled variables in s2

If i grab the url that is sending them from s2 to s1 and paste it in the browser and load it manually it works.

What am I missing?

Thank you for any ideas and help.

If i grab the url that is sending them from s2 to s1 and paste it in the browser and load it manually it works.

Ok, I think this is the most important observation here.

So passing the variables on to the survey mid survey works (my initial thought was that the issue might be because LS is not picking up the variables if it is not at the start of a survey, which obviously is not the case based on your description).

So there is something different between a redirect and copying and pasting. What happens if you click instead of an automatic redirect?