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A GAO report on NASA's ongoing projects can be found here. On page 70 while discussing the Lucy mission, it says

the ... main engine was the same model used on a series of environmental satellites that have had engine performance problems. The engine has failed in flight more than once and was a single point failure for the Lucy project. As a result, the project completed an engine trade study in July 2017 and decided to select a different engine.

What were the "series of environmental satellites" the report is referring to, and what was the engine?

Organic Marble
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    This is a puzzler. The GAO report notes Lucy as sharing architecture with MAVEN and Juno. The Leros engine used on Juno has had problems both on that mission and Intelsat 33e, but those aren't environmental sats. GOES-16 (aka GOES-R) uses Leros but didn't have a propulsion failure. MAVEN uses MR-107N, which is the thruster of choice for Mars landings; AFAIK it doesn't have any notable failures in its history. – Russell Borogove Feb 01 '19 at 15:58
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    It's certainly not out of the question that the GAO is wrong. It's difficult to search for vague stuff like "a series of environmental satellites that have had engine performance problems"! Would it have killed them to name the engine.... – Organic Marble Feb 01 '19 at 16:22
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    MR-107 is unlikely; it's a low-specific-impulse monoprop thruster, and Lucy needs a lot of ∆v. If I had to bet I'd say Leros, since it's had valve problems. – Russell Borogove Feb 01 '19 at 16:30
  • @RussellBorogove I ran across this answer: https://space.stackexchange.com/a/21621/6944 which makes me think you're right that it's Leros and the GAO is a bit confused. If you want to write that up I'll accept it. – Organic Marble Jul 14 '19 at 13:46

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