[FS#1543] Many packages in snapshot failing on one build, ok on next but no code changes.

[LEDE Bugs]

The following task has a new comment added:

FS#1543 - Many packages in snapshot failing on one build, ok on next but no code changes.
User who did this - Rob White (bluewavenet)

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A long story, so I will try to keep it short.
I noticed this after one of my custom image builds began having a problem with lighttpd after 25th April (LEDE 17.01.4)
The version in snapshot should have the fix but a line in Makefile was missed out. 
I noticed lighttpd was missing in snapshot/packages so looked at faillogs and found many errors.
However later the faillog was different and in fact seemed to change every time the build system re-ran.
I looked at other packages and found the same pattern of apparently random things happening.
The other day lighttpd re-appeared in snapshots, but later failed again (but no changes in the code).
This morning it was back again.
I tried resubmitting my previous PR and Travis failed again (with different errors yet again).
Looking at faillogs for many other packages I can see similar things going on.

I might be misunderstanding how this all works, but it seems to me to be a package will fail to build if a dependency has also failed, which seems reasonable, but this seems to be leading to the build system chasing its tail, or somehow there was a "storm of errors". 
Here is my last Travis log:
https://travis-ci.org/openwrt/packages/builds/377700000

My past experience in IT support made me imagine maintainers tearing their hair out trying to fix something causing this, hence my initial sketchy ticket details. If I am doing something wrong, or there is something wrong with the package, then I can look in depth there, but the same pattern seems to appear in the faillogs for other packages...

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More information can be found at the following URL:
https://bugs.openwrt.org/index.php?do=details&task_id=1543#comment4712