Created attachment 155822 [details]
show the location of problem
when I switch Impress in presentation mode, the zoom in out zoom out button make the presentation switch to another slide.
This may (or may not) be another duplicate of bug 127921, like bug 127012.
Please test if it's fixed in 126.96.36.199 available now: https://www.libreoffice.org/download/download/?version=6.3.4
You may also wait a few days for 188.8.131.52, that's published as 6.3.4, how it suits you.
Let's close as a duplicate, like bug 127012.
*** This bug has been marked as a duplicate of bug 127921 ***