Upgrading from PostGIS 2.5 to PostGIS 3.1 - calling two set returning functions in a UDF is 7x slower

Question

I'm migrating our PostGIS 2.5 stack to PostGIS 3.1. In general it's been really smooth - a few of our operations on larger geometries are much faster, and the rest of our performance is about the same. The one snag is that one of our user-defined functions is now taking 11 seconds to run, when it previously took 1.5 seconds. Here's an MWE:

-- create initial geom table of a large rectangle over Kansas & Nebraska in the US
create table _tmp1 as
select st_setsrid(st_geomfromgeojson('{"type":"Polygon","coordinates":[[[-104.4140625,37.78808138412046],[-94.74609375,37.78808138412046],[-94.74609375,42.09822241118974],[-104.4140625,42.09822241118974],[-104.4140625,37.78808138412046]]]}
'), 4326) as geom;

-- duplicate this geom into a bunch of additional rows to better compare performance
insert into _tmp1 (geom)
SELECT geom FROM _tmp1 CROSS JOIN generate_series(1,1000) as x;

-- create our MWE function- much simpler than the actual code
create or replace function st_dump_mwe(geom geometry)
  returns geometry
  language sql immutable as
$func$
      select (ST_DumpRings((ST_Dump(geom)).geom)).geom;
$func$;

When I call this function in PostGIS 3.1 via select st_dump_mwe(geom) from _tmp1;, it takes ~11 seconds. In PostGIS 2.5, it takes 1.5 seconds.

PostGIS 3.1 full version:

 POSTGIS="3.1.0 5e2af69" [EXTENSION] PGSQL="130" GEOS="3.8.0-CAPI-1.13.1 " PROJ="6.3.1" LIBXML="2.9.10" LIBJSON="0.13.1" LIBPROTOBUF="1.3.3" WAGYU="0.5.0 (Internal)"

PostGIS 2.5 full version:

 POSTGIS="2.5.5" [EXTENSION] PGSQL="130" GEOS="3.8.0-CAPI-1.13.1 " PROJ="Rel. 6.3.1, February 10th, 2020" GDAL="GDAL 3.0.4, released 2020/01/28" LIBXML="2.9.10" LIBJSON="0.13.1" LIBPROTOBUF="1.3.3" RASTER

Both versions are running locally on my machine in Docker and were installed with the standard postgresql-13-postgis-3 and postgresql-13-postgis-2.5 ubuntu packages.

Any idea what's going on here? Are these changes expected?

Finally, are there any external resources that cover potential pitfalls associated with this upgrade? I've read the v3.0 changelog but haven't been able to identify where this might originate.