That is very weird with the glue not holding, this stuff normally would support an elephant, I know there was talk of some knock off branded E6000 around which had was of a lesser quality. I am also wondering about the age of the glue, I had a tube I kept forgetting to use and over time it went a little opaque and was not as strong as other tubes I have used.
A thread on the issues of E6000 https://www.whitearmor.net/forum/topic/49246-e6000-original-vs-fake/
Some web info on knock off branded E6000 https://www.e6000.com.au/e6000-blog/did-i-buy-genuine
Coming along nicely.