Joomla 3.8.5 CiviCRM 4.7.29 PHP 7.0.7 I have four contribution pages for different membership levels, Bronze, Silver, Gold and Platinum. Everything seemed to be working and I had members signed up through all four pages. At some point, not sure when, three of them stopped working - Bronze, Silver and Platinum. I only found out because potential members emailed me to tell me they couldn't access the pages. I checked from the front end by selecting the appropriate menu items and found that only the Gold went to a contribution page, the other three only produced a blank whit page. I can't find anything in the log that helps.
Ok, so here is where I am after some head scratching and some inspiration from @IowaBoy. All of my contribution pages are now working, having recreated the problem ones from scratch instead of copying a working one. All of the contribution pages that had problems were created about a year ago and they were working as we had membership sign-ups from all of them. I now think that they stopped working after my upgrade from CiviCRM 4.7.27 to 4.7.29. I suspect this as that I started receiving notifications about the problem some time after the upgrade.
In my investigation of the problem, I verified that a new test contribution page made by copying the working one also did not work. I further verified that a new test contribution page made from scratch worked as expected. I have recreated our non-working contribution pages from scratch and so far they seem to be working. I stronly suspect that something in the 4.7.29 release has broken the process of creating a contribution page by copying. Thanks to IowaBoy for stimulating my thinking process.
Can I make a suggestion, as i had a similar issue and it showed up after the upgrade. I had to modify the user.ini from PHP to give more resources, and voila! It mas magic everything came back. I bumped up a few things while I was at it: max_execution_time is now at 90 max_input_time doubled it to 180 I think the max_execution_time was it, and civi just needs more time in the newer versions. We're at now 5.11.0 on joomla, and just love it. Been using it for a few years now.