Hcg line progression regression. Thoughts?

This is my 10th pregnancy (I have a nine year old and 3 year old, rest were miscarriages that on average make it to week 10-11). Years ago I had a chemical where one day I had a faint positive and the next it was gone and my period started late. This time I have the slow line fade over the last 2-3 days. These are Wondfo 10u/ml and early detection internet cheapies. Top is Friday 10 dpo the 27th in the evening (blood draw that day: hcg at 40). The middle is the 28th and the bottom is today the 29th. Chemical?