Windower Running Very Slowly Even With No Plugins

Starting a couple weeks ago, FFXI w/ Windower started running much slower than normal. This ranges from about 15-20 FPS in most zones, to 3-5 FPS in certain other zones, even with everything turned down to minimum and nothing happening. In comparison, I used to get 25-30 FPS everywhere even with everything set to max.

This occurs regardless of whether I have any plugins or addons loaded, and gets instantly fixed whenever I load FFXI without Windower.

I'm running on Windows 10 (version 1709, build 16299.125) currently. I don't remember the slowdown starting right after an update, but I could be remembering wrong.

Task Manager doesn't detect anything untoward, and I'm stumped. Does anyone have any ideas what might be going on, and if there's anything I can do to fix it other than maybe waiting for an update?