through the test, we found the following facts
Note: conclusion passed the official demo test, https://ueditor.baidu.com/web., https://ueditor.baidu.com/website/umeditor.html

1. safari on the real machine iOS12 supports both ueditor and umeditor
2. Wechat's browser on the real iOS12 does not support ueditor, but supports umeditor
3. Wechat Web development tool supports both ueditor and umeditor

so the advice is not to go head-to-head with ueditor and switch to umeditor or other actively maintained editors.
the exact reason is not clear.

after testing, it is found that the reason is that Ueditor runs Iframe, on the real machine iOS12, and Wechat browser does not support it!
modify as follows:

find the location of 6939 lines of code (as shown in the following figure, which is the effect of the code before modification)

6940 6939 :

setTimeout iframe :

:

tested to be feasible!