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Your LimeSurvey version:   LimeSurvey Cloud Version 5.6.54
Own server or LimeSurvey hosting:  LimeSurvey hosting
Survey theme/template: fruity
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UPDATE:   Issue resolved.   'Error' messages for standard themes in Themes section disappeared,  I've re-installed them, everything is working.  

My active surveys stopped working, and even List Surveys page is not available (says 'Could not find a working installed template').    I've received notifications that used themes are not compatible with current version - all themes I see listed in Themes section (bootswatch, fruity, fruity_twentythree, vanilla) show 'Error' message.   I'm using a Cloud version in browser and have used 'fruity' theme when setting up surveys. Please advise what should be done to get access to existing surveys and update them with new themes - would it be possible to do without losing the data? 
 

> UPDATE: Issue resolved. 'Error' messages for standard themes in Themes section disappeared, I've re-installed them, everything is working.

How do you do this ?
How this issue happen ?

How this issue happened: There was no action on my side leading to this issue. When learning that links to my active surveys suddenly stopped working, I checked the admin module and identified that 'List surveys' page is not available, and saw pop-up messages in admin module for each of standard 4 themes that they are 'not compatible with current version'. 'Default theme' field for my account became empty. And at 'Themes' page, it was not possible to re-install any of 4 standard themes (vanilla, fruity,...) - as all of them were showing red 'Error' signs, and 'Install' button was not active. Then, after a while, I assume that this issue was corrected by LimeSurvey team - as these 'Error' signs disappeared, and I was able to re-install standard themes (pressing 'Install' button) - after that, 'List surveys' page showed my surveys and active survey links started to work again. So it looks to me that the Cloud browser version update has broken my active surveys, but later the error leading to this was corrected, and I was able to run my active surveys again.

Thank you !