The ongoing quest for understanding nonequilibrium dynamics of complex
quantum systems underpins the foundation of statistical physics as well as the
development of quantum technology. Quantum many-body scarring has recently
opened a window into novel mechanisms for delaying the onset of thermalization,
however its experimental realization remains limited to the $\mathbb{Z}_2$
state in a Rydberg atom system. Here we realize unconventional many-body
scarring in a Bose--Hubbard quantum simulator with a previously unknown initial
condition -- the unit-filling state. Our measurements of entanglement entropy
illustrate that scarring traps the many-body system in a low-entropy subspace.
Further, we develop a quantum interference protocol to probe out-of-time
correlations, and demonstrate the system's return to the vicinity of the
initial state by measuring single-site fidelity. Our work makes the resource of
scarring accessible to a broad class of ultracold-atom experiments, and it
allows to explore its relation to constrained dynamics in lattice gauge
theories, Hilbert space fragmentation, and disorder-free localization.