This is a restatement of the problem the guy from Japan is experiencing:
Under Win10, using the Text and Overlay HTML over one clip, both filter results are visible. An exported frame shows both results. Exporting the clip shows only the Text result and not the Overlay HTML result. The test clip is a block of white.
I tried to reproduce the problem: text & overlay over ten second white block. Problem not found.
Obviously some step is being missed in the OP’s procedure. I have no idea what that step is.