with newest release (1.35.0-wmf.19), it seems that gallery slideshow stopped working
when not wrapped in a block element with "max-width", "min-width". or "width" style defined.
untilbefore this version, it was enough to have a:
```
<gallery mode=slideshow>
file | description
....
</gallery>
```
for gallery to actually show a slideshow. from this version, it seems that it became essential to either add style with set max-width to the gallery tag, or to wrap it inside a div with max-width value, like so:
```
<gallery mode="slideshow" style="max-width:438px">
file | description
....
</gallery>
```
or like so
```
<div style="max-width:438px">
<gallery mode=slideshow>
file | description
....
</gallery>
</div>
```
otherwise, no slideshow.
this is not documented anywhere, and i find it hard to believe it's the intended behavior.
NOTE:
naked gallery slideshow tag _did_work (i.e., displayed a slideshow) with previous version (i think 1.35.0-wmf.18)
verified with chrome ( 79.0.3945.130), firefox (73.0.1) and edge (44.18362.449.0).
peace.