The initalization of top in the template function OCL4DNNConvSpatial<float>::verifyResult is errant.

That code is a noop. It does nothing. Why? Because there is no member function zeros(). Instead there is a static function UMat::zeros(). C++ allows you to call the static using the dot. The static function returns a UMat. It does not alter a UMat itself. Therefore, the initialization function runs, creates a new UMat, and then discards it. top is never changed. This is a coding error that CV_NODISCARD would catch ;-)

Might be part of #18457. I have the same failure in mapping of that issue. While debugging, I found the above errant code.

If you want to initialize top with zeros, correct code is

top = top.zeros(4, sz, (use_half_) ? CV_16SC1 : CV_32FC1);
// or the equivalent
top = UMat::zeros(4, sz, (use_half_) ? CV_16SC1 : CV_32FC1);

System information (version)

• OpenCV => 3.x and 4.x
• Operating System / Platform => all
• Compiler => all

Issue submission checklist

• I report the issue, it's not a question
• I checked the problem with documentation, FAQ, open issues,
  forum.opencv.org, Stack Overflow, etc and have not found solution
• I updated to latest OpenCV version and the issue is still there