Hello,
after upgrading our Piwik installation to 2.11.2, we receive the following Warning regarding htmlspecialchars() function:
WARNING: /software/frmtools/sunos5.10-x64/piwik/piwik-2.11.2/vendor/twig/twig/lib/Twig/Extension/Core.php(1007): Warning - htmlspecialchars() [function.htmlspecialchars]: Invalid multibyte sequence in argument - Piwik 2.11.2 - Please report this message in the Piwik forums: http://forum.piwik.org (please do a search first as it might have been reported already)
The problem was already mentioned some time ago, although in different files, see 301 Moved Permanently and Warning: htmlspecialchars(): Invalid multibyte sequence in argument in piwik/vendor/twig/twig/lib/Twig/Extension/Core.php · Issue #5157 · matomo-org/piwik · GitHub.
If you need any further information, please let me know.
Best regards,
Maik