The only limiting thing I've experienced with ActiveRecord is when the database becomes larger and more complex. The performance takes a bit of a hit. Which isn't ActiveRecords fault, it's the developer's lack of understanding how the database works.
Most of the issues I see is a lack of understanding of things like N+1 queries. I see this mistakes from junior to senior level. ActiveRecord has built in solutions to fix them too. Some developers don't know about them.
There are built-in solutions but also quite severe limitations when you get to advanced usage of activerecord. Especially with regards to composability. Of course, raw SQL is also really bad in that scenario.
Most of the issues I see is a lack of understanding of things like N+1 queries. I see this mistakes from junior to senior level. ActiveRecord has built in solutions to fix them too. Some developers don't know about them.