Hi,
I've seen this on Kodi 18.8 (OSMC) on my Raspberry 3: the Confluence Skin and the OSMC default skin do have what it seems to be the right beaviour while Estuary still has the issue.
Looking at the skin source I've noticed that Estuary has, in the xml/Defaults.xml file, the following configuration:
xml:
<default type="multiimage">
<aspectratio align="center">scale</aspectratio>
<fadetime>800</fadetime>
<timeperimage>7000</timeperimage>
<randomize>true</randomize>
</default>
I don't know if this section is still the right one for the slideshow (but
multiimage documentation suggests so). If it is, then fadetime and timeperimage might be somehow messing with the slideshow configuration.
Those options are missing from Confluence skin since it has no "multiimage" type 720p/Defaults.xml file.
OSMC default skin has in xml/Defaults.xml file:
xml:
<default type="multiimage">
<include>WindowDepth</include>
</default>
Hope this can be of some help.
Regards