Adding one more observation:
When I compare the HTML source for my working 2.0.5 Pawtucket install with that of the 2.0.6 Install (that does not work) it appears that the HTML for the head for the latter is generated fine---except for the "</head>" part. The HTML source code abruptly stops after
<script type="text/javascript">
jQuery (document). ready(function () {
jQuery ('#browse-menu').on( 'click mouseover mouseout mousemove mouseenter'
, function(e) { e.stopPropagation(); });
});
</script>
In the code for my 2.0.5 install this is followed by </head> and then "<body>...</body>" etc. I would say this means there is a problem with the php code right before "</head>" is to be printed. But then, I do not really know much about php programming. Also, I did composer up on both installs and the only potentially noteworthy message was that 2.0.5 apparently uses three abandoned packages: laminas/laminas-zendframework-bridge, maximebf/debugbar, and php-debugbar/php-debugbar. It appears 2.0.6 no longer uses these packages.
Thanks,
Eisso