slideshow cycle failure with error message after update to 7.x-3.4

I have the same error message and have reverted also.

There is no automated testing suite with the 7.x version of Views Slideshow. I added a minimal one to the Drupal 8 version last year. Manual testing was done but unfortunately manual testing cannot test all possible set-ups easily :(
Thanks for the report, investigating.

hmm interesting... totally can't replicate it so far :(
However I have ideas.
Information/background:
- The main slideshow theme preprocess function, sets rendered_rows to '' (blank string).
- The main slideshow theme preprocess function, then appends further strings to it.
- The main slideshow template then renders it.
- No changes to the template other than docstrings were made between 7.x-3.2 and 3.4
- Minimal changes to the preproces function were made and none that *should* affect that variable.
- However, the HOOK_theme() implementation was changed to properly call the theme functions in the theme/views_slideshow_cycle.theme.inc file instead of the somewhat "wrong" method that was used previously of having a template_preprcess_THEMEFUNCTION() in the main module file that was calling the functions in that theme file. This is working fine under my testing (and a production site of mine) and theoretically/experientially for many other modules/situations. However; this is a change of an aspect that is often cached, so if someone experiencing that could clear all caches and test again that'd be great.

TLDR: Clear all caches and try again. If that fixes it, I'll add a update function that forces a cache clear.

In my case clearing the cache fixed the error. I would have sworn that I had already done that, but apparently not.

Easy to forget to clear the cache ;)
I'll add a forced clear to ensure safety, Thanks.

If you are running APC make sure you clear that cache too.

E

Thanks @NickWilde. Clearing cache fixed the problem.