  Accretion discs in active galactic nuclei (AGN) foster black hole (BH)
formation, growth, and mergers. Stellar mass BHs migrate inwards under the
influence of hydrodynamical torques unless they encounter a region where the
torque flips sign. At these migration traps, BHs accumulate and merge via
dynamical or gas-assisted interactions, producing high-frequency
LIGO/Virgo/KAGRA (LVK) gravitational wave (GW) sources and potentially cutting
off the supply of extreme mass ratio inspirals that would otherwise make
low-frequency, {\it LISA}-band GWs. In this paper, we study the interplay
between different types of migration torques, focusing especially on the
``thermal torques'' generated by the thermal response of the AGN to embedded
stellar-mass BHs that accrete through their own mini-discs.In contrast to
previous work, we find that Type I torques cannot produce migration traps on
their own, but thermal torques often do, particularly in low-mass AGN. The
migration traps produced by thermal torques exist at much larger radii ($\sim
10^{3-5}$ gravitational radii) than do previously identified Type I traps,
carrying implications for GW populations at multiple frequencies. Finally, we
identify a bifurcation of AGN discs into two regimes: migration traps exist
below a critical AGN luminosity, and do not at higher luminosities. This
critical luminosity is fit as $\log_{10} L_{\rm AGN}^c = 45 - 0.32
\log_{10}{(\alpha/0.01)}$ where $\alpha$ is the AGN alpha viscosity parameter,
a range compatible with recent claims that LVK GWs are not preferentially
associated with high-luminosity AGN.
