Dokuwiki 2014-09-29d "Hrun" (Debian package), various installations with various plugins. epub 2015-02-15.
Javascript console message "Uncaught ReferenceError: Invalid left-hand side expression in postfix operation" (minify error?)
This is a recent event, likely the result of upgrading other plugins, however 1x1 didn't show which one - only that removing or downgrading epub make the toolbar reappear.
The problem does not occur when using Konqueror web-browser.
Rolling back to the 2013-02-08 version of epub brings back the edit toolbar.
You don't say which browser you are using when the error occurs. I ran it in Iceweasel on Debian without a problem. But my Iceweasel is old.
Have you tried unloading all the other plugins except epub?
Disable compression and see if you can find where the error occurs. The current error message is not specific enough, since it doesn't give the location of the error.
Between the current version and feb 2013 there have been about 50 commits, so knowing that it worked 2 1/2 years ago doesn't really help narrow things down.
It's also possible that there is something in one of the pages that you are saving to your ebook that is causing this. So that would require a separate investigation.
Edit: Just ran current version of Iceweasel on Debian 7, again without a problem. The above was Debian 6.
Dokuwiki 2014-09-29d "Hrun" (Debian package), various installations with various plugins. epub 2015-02-15. Javascript console message "Uncaught ReferenceError: Invalid left-hand side expression in postfix operation" (minify error?)
This is a recent event, likely the result of upgrading other plugins, however 1x1 didn't show which one - only that removing or downgrading epub make the toolbar reappear. The problem does not occur when using Konqueror web-browser. Rolling back to the 2013-02-08 version of epub brings back the edit toolbar.
Example of other plugins used in an installation: abbr 2014-08-18, acl 2014-06-04, ajaxloader 2009-12-11, alphaindex 2008-10-18, authad 2014-04-03, authldap 2014-05-18, authmysql 2014-02-15, authpgsql 2014-02-15, authplain 2014-07-01, blockquote 2013-05-05, bookcreator 2015-06-11, bureaucracy 2015-01-22, cellbg 2013-10-09, columns 2015-05-30, config 2014-03-18, data 2015-05-16, dig 2015-02-26, do 2014-11-01, dw2pdf 2015-06-25, edittable 2015-06-17, epub 2013-02-08, extension 2014-06-15, fancysearch 2015-02-26, fckg 2014-12-15, fontsize2 2010-03-26, gallery 2014-05-18, hidden 2015-08-21, imagemap 2015-08-13, imgpaste 2015-02-26, info 2014-03-05, konsole 2015-08-18, log 2015-02-26, nslist 2015-02-26, odt 2015-02-26, pagebreak 2015-07-13, pagemod 2014-11-10, pagenav 2015-02-26, popularity 2013-10-14, qc 2015-06-17, revert 2013-11-21, safefnrecode 2012-07-28, searchpattern 2013-06-16c, sqlite 2015-05-04, todo 2014-11-26, toucher 2012-09-16, usercontact 2015-02-26, usermanager 2014-03-05, wikipediasnippet 2013-04-06, wrap 2015-07-19