I don't believe this. Nearly anything complex and networked, after a few months investigation by a good security professional, will have a good number of exploits found.

These could be plain old bugs, or they could be planted backdoors. (usually indistinguishable)

Even after months of effort, there is a high probability there remain undiscovered security issues (either deliberate or accidental) that more effort would have found.

For that reason, I don't believe any claim when they say "nah, we couldn't find anything". They either didn't look, or don't want to reveal what they found.

Further, when America's anti-Huawei panic started HMG were looking for an excuse to ban Huawei kit. If problems had been found it's likely they would have been mentioned.

That's not true. GCHQ looked at source that was provided and found many unpatched vulns, and then found that the firmware binaries were not matching the source that was provided (with a single exception), so only Hwawei really knows what their devices do.

Unless you have access to secret information and are for some reason burning your life down on HN, you have no idea what they found or didn’t find.