  Quantum information transport over micron to millimeter scale distances is
critical for the operation of practical quantum processors based on spin
qubits. One method of achieving a long-range interaction is by coherent
electron spin shuttling through an array of silicon quantum dots. In order to
execute many shuttling operations with high fidelity, it is essential to
understand the dynamics of qubit dephasing and relaxation during the shuttling
process in order to mitigate them. However, errors arising after many repeated
shuttles are not yet well documented. Here, we probe decay dynamics
contributing to dephasing and relaxation of a singlet-triplet qubit during
coherent spin shuttling over many $N$ repeated shuttle operations. We find that
losses are dominated by magnetic dephasing for small $N<10^3$ and by incoherent
shuttle errors for large $N>10^3$. Additionally, we estimate shuttle error
rates below $1\times10^{-4}$ out to at least $N=10^3$, representing an
encouraging figure for future implementations of spin shuttling to entangle
distant qubits.
