Text entries of plugins such as xfce4-dict and xfce4-calculator-plugin used to have visible (and blink) carets, not anymore with panel 4.13. I didn't investigate this properly, but it seems gtk2 plugins are also affected.
Sounds like a potential theming issue. I personally don't use any of the aforementioned plugins - is the same true for Adwaita?
As you probably have guessed I'm using Greybird, and indeed it looks like a theme issue, with Adwaita the caret works fine. Closing in favor of this Greybird issue: https://github.com/shimmerproject/Greybird/issues/241