ADG lag after upgrading to 12.1

After upgrading to 12.1.0.2 from 11.2.0.3 on our primary and ADG physical standby, I started seeing lag. The standby is on the same box, used for ad-hoc reporting. Prior to the upgrade, 99.99% of all lag was 7 seconds or less over the past 12 months. After the upgrade, it's 6 minutes.

This wasn't totally unexpected, thanks to Neil's blog post https://chandlerdba.com/2019/01/03/data-guard-unexpected-lag/ and this list. After recreating the Thread 0 standby logs to be in Thread 1 about 15 hours ago, the lag has improved dramatically, as hoped. However, I'm still regularly getting lags of 20-30 seconds, whereas in 11.2 that was a rare occasion.

This isn't a show-stopper by any means, but I want to find out why the lag is still higher than in 11.2, in case it's an indicator of a configuration issue or bug.

I'm not sure where to start looking. Any ideas?

Thanks,
Rich

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