Which version of Lightroom do you have?
Which operating system : Windows or mac?
Does that happen only in developing module while switching photo or in Library module as well?
It seems to really only be affecting files while trying to edit in the develop module, or even just viewing from photo to photo in the develop module. Lightroom CC (it is completely up to date) and MAC - we've used LR for years on hundreds of events, I've never seen anything like it - it is tripling the amount of time it takes to edit a single photo. Thanks!
Thanks for the update.
Would suggest you to reset Lightroom Preferences : Resetting (or 'Trashing') the Lightroom Preferences file | Lightroom Forums
and if that does not help, go to Lightroom Preferences > Performance > uncheck "use graphics processor" and then, check.