As a test, I called al_acknowledge_resize even when the window had not actually been resized and when it was in windowed mode, and it killed my font. I didn't have any other bitmaps yet so I didn't notice anything (the rest is draw via primitives calls).
This may be partially my fault, because if I wrap the al_acknowledge_resize call with a condition (for example on a key down event), it works. I actually was testing whether or not I really needed to listen for resize events and call resize -- if I could just call it every loop, since on every loop I already call al_get_display_width and al_get_display_height and set a transform to scale the "fixed" game to the window. I should try legitimately listening for the resize event and only calling ack then to see if there are any problems.
I also tested this with a normal load_bitmap call loading a JPG and saw the same results. Interestingly in one test Windows 10 said my NVIDIA windows kernel driver crashed and it restarted it.
I'm willing to try any version of Allegro but I'm working from my jalleg library and trying to call every module, so I don't have any C compiler, plus I've heard the dependencies build on Windows is quite involved. I didn't see any 5.2.1 snapshot on GNA.