Post any defects you find in the released or beta versions of the ImageMagick software here. Include the ImageMagick version, OS, and any command-line required to reproduce the problem. Got a patch for a bug? Post it here.
I updated ImageMagick-7.0.4-Q16 to ImageMagick-7.0.8-Q16 and I using it for Lightroom plugin LR/Mogrfiy 5.10. In updated version 7.0.8 overlay modes (soft light, linear light, etc.) are not working - they export always as normal overlay. I also tried older version ImageMagick-6.9.10-Q16 and it works OK, so it should be bug related to latest version.
Which exact version of IM 7.0.8.x are you using and on what platform/OS? The current version is 7.0.8.34. If you are not using it, then try upgrading to that or the most current one and see if that works.