The large $\eta'$ mass depends on the topological properties of the QCD gauge fields and an accurate measurement requires an ensemble that well samples the possible topologies of the gauge fields. In this proceedings, we present our analysis of the RBC-UKQCD $24^3\times64\times24$ physical coarse DWF ensemble. The evolution of the global topological charge is measured using the 5-loop improved method [1] after cooling via Wilson flow. The results for closed quark loops, which are sensitive to the topology on the original (unflowed) configurations, are shown to have long autocorrelations. Several eigenvectors with small eigenvalues are calculated for one specific configuration and topological fluctuations are found. Preliminary calculation of the $\eta$ and $\eta'$ mass is done. Our results show that good sampling of the global topological charge (measured after the Wilson flow) does not necessarily mean rapid evolution of local topological fluctuations.