Never had any issues with CyberPower UPS.
Have over a dozen of those UPSs in service at various locations for several years now, including my home...not a single issue.
That glue is used on many other things, emergency lighting, industrial electronics, robotics....even other UPS brands.
I see no evidence of a wide spread issue in regards to that glue being used.
The discoloring, i suspect would be due to heat.
I suspect the small amount of users that had their unit fail, used generic, cheap battery replacements from third party sellers.
I have nothing but issues with APC, never had a APC unit last more than 2yrs, one even caused a small fire at a previous workplace. APC denied there was a fault, and refused to honor their warranty or pay for damages. The business had to sue them, i never found out how that went though.
CyberPower is local to me here in MN, their headquarters.
I can just walk into their headquarters and deal with them direct if i should have any issues.
APC, is overseas.