Thumbnails no longer showing on page

You seem to have added a lazy-loading plugin, which is replacing Photonic’s images with its own. You will need to disable that plugin. Photonic handles its own lazy-loading and optimization.

There always has been a lazy loading plugin, wp rocket. Nothing had changed. Just the wordpress update.

I can tell you for a fact that it is the lazy loading that is breaking Photonic behaviour. Whether it is from WP Rocket or elsewhere, you know best.

I can also tell you for sure that whenever a plugin replaces Photonic’s thumbnails with an abstract GIF (which in your case is data:image/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==), it will break Photonic. This has been the case for at least a few years.

Since you say you use WP Rocket, here is their documentation for reasons for incompatibility. They cite “JavaScripts that try to calculate spaces based on image size” as one of the reasons, as well as “Grid layouts that use fixed positioning/fixed widths”. While I am not sure what code they have, I can tell you that depending on which layout you are using on Photonic, you will likely encounter one of these scenarios.

They also say that they automatically disable themselves for some plugins. In this list there are plugins like “Justified Image Grid” and “Envira Gallery”. Knowing what I know of gallery plugins and layouts, I am fairly certain that the backbone for layouts is going to be very similar, so disabling would be needed for Photonic as well.

At the end of the day, it is best to rely on native browser based lazy-loading rather than custom solutions. This is widely supported by browsers for more than 99% of users.