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Your LimeSurvey version: Version 5.3.9+220411
Own server or LimeSurvey hosting: own
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I am facing this issue and I would like to share it here. 

For example I have a question which is shown only for specific conditions. I add these conditions using conditions designer and it all works fine. Whenever I open the question and "Save & Close" it, if I go to condition designer the conditions are gone. I cannot edit them in the condition designer anymore. I only can edit in the Condition field in General Settings of the question. This is not friendly. Is there any way the conditions could stay in the condition designer? Is this a bug or maybe a "missing" feature of the platform?

Your feedback is really appreciated! 

Thank you in adcance!

That looks like a bug. The condition designer is having a hard time recently. I see no fixes in the current release of version 5.X. So you might report that behaviour as a bug via the bugtracker.

Hm, strange, 
I tested in 5.3.10.
1. Created a condion with condition designer
 

2. The condition is there
 

Saved and closed the question

3. When I open the condition designer again, the condition is still there
 

4. and after a click on the pencil I can edit
 

Probably I misunderstood your issue.

By the way:
Using the "condition" field in "General settings" is much more effective, more flexible and with much more options.
Try to do this with the condition designer:
((Q1==1) AND (Q2_SQ001=="Y" AND Q2_SQ003=="Y") OR (Q2_SQ004=="Y" AND Q2_SQ005!="Y")) AND sum(that.Q4.NAOK)>20
In the field you just enter this.

Joffm