Attempting to fix issue 1084, we accidentally broke users on older versions of protobuf. In addition, issue 1083 introduces additional breakage that v29.0.0 doesn’t address.
As a result, v29.0.0 is broken for usage with protobuf versions below v4.31.0.

It also seems like there may be an additional issue as pointed out in at the end of issue 1084.

We are going to be deprecating v29.0.0 of the library, do not use it.

V30.0.0 will be released soon, in it we will pin the dependency as "google/protobuf": "^3.21.5 || >=4.26 <=4.30.0".
We will also revert back the src/Google/Ads/GoogleAds/Util/FieldMasks.php file to use the formerly supported $fieldDescriptor->getLabel() === GPBLabel::REPEATED instead of the newly introduced isRepeated() method in v31.0 of protobuf.

At that time, any users on v29.0.0 should upgrade to v30.0.0 AND do a clean dependency installation to ensure the new protobuf versions are picked up.

We will lift this restriction in a future version (once v30.0.0 is released, we will create a new bug and pin it to track the fix for this issue.