There are no technical related issues. Generally, it's normal to see fluctuations in your sub count. This is because we want to make sure the numbers are 100% accurate, so we perform additional verification & spam reviews.
This is actually a normal part of how YouTube validates views. Temporarily slowing down or even freezing a video's view count is expected, here are more details about why this happens and how it works: https://goo.gl/S7DIry