Hello, since upgrading to version 1.5.6 (and then further to 1.5.7) the little buttons that used to have about five resolutions under the photo displayed are missing. I have toggled their representation from buttons to I think it was a dropdown list, but nothing reappeared. I am using the default theme included in zenphoto, called zenpage. Have tried switching to a couple of other ones that are included by default without luck. Any ideas on what could bring those buttons for controlling the viewed size back? Thanks!

That's because the plugin viewer_size_image was removed in version 1.5 (may 25, 2018)
See https://www.zenphoto.org/news/zenphoto-1.5/#--removed-plugins

Oh, thanks fretzl for taking time to bring that change to my attention. I quite liked that option and thought something was broken and repairable. Cheers!