We have now opened a commercial services section here on the forum for registered users. If you have a Fabrik project that you wish to have someone work on for you, post it under Help Wanted. If you are an application developer and wish to earn some money helping others, post your details under Fabrik Application Developers.
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For running J!5.1 you must https://fabrikar.com/forums/index.php?wiki/update-from-github/ or include the new file manually https://fabrikar.com/forums/index.php?threads/joomla-5-1-and-fabrik-cannot-find-files-error.54473/post-285151 See also Announcements
My search through the commit log was looking for anything with filter, so I didn't see this one. However, this fix was applied to the master branch in Nov 2017 and so will presumably already be included in @stevelis' update from Github.There was a fix in GitHub which may address this issue
https://github.com/Fabrik/fabrik/commit/392b5a9c18f0db583933920ad281ab0e144c7826
seems this is creating a different "filter-grouped" string in the list paramsand the rest is in the JS file for the pre-filter tab on the back-end which handles adding new pre-filter rows,
yesAnd you will need to re-save the List as well I think.