Having several keyboards won't allow me to dictate to iPad properly

I have several keyboards installed on iPad. when I try to dictate using them, as for example in Facebook, the only result is a string of gobbledygook. At present, I have three keyboards installed, but having only three does not get rid of the problem. It seems that the only way to ensure that I can dictate, and ensure that what I dictate appears on the iPad as it should is to get rid of all extra keyboards.

My iPad is about 4 years old, and is a 2nd-generation 12.9 inch iPad Pro.

1) Does anyone else have this problem ?

2) Is there any means by which I can have several keyboards installed, and also use dictation without this problem recurring ?

Thank you in advance.