I have a big problem with LAMP. My negative controls have a band without DNA samples and my positive controls don't appear bands. Both my negative and positive control only has a band about 100bp. I'm performing LAMP follow protocol of NEB LAMP and I tried to optimize temperature, time incubation of reaction, I also added betaine but this band don't remove and positive control don't have bands as expected result. I ordered a different set of primer but this problem is still unchanged and removed contamination cases. Could you give me some advices? I really need everyone's help.

P/s: My problem is as below the picture. I use ladder 100bp