We made some changes in v1.5.3 b5238 that we hope will improve this. However, we’re not sure we really found the root cause.
Please try the new version and let us know if things have improved. If the application still gets sluggish after long use, it’d also be worth trying what @24pdailies mentioned above:
It’d be helpful to know if that does help in this case, or if you need to restart the application to get things back to normal.