Loss is not decreasing

loss is not decreasing, and stay about 10
training is based on VOC2021 images (originally 20 clasees and about 15000 images), i added there 1 new class with 40 new images.
i use:
ssd_inception_v2_coco model.
Python 3.6.13
tensorflow 1.15.5

I have to use tensorflow 1.15 in order to be able to use DirectML because i have AMD GPU

followed this tutorial: