UltiMaker uses functional, analytical and tracking cookies. Tracking cookies enhance your experience on our website and may also collect your personal data outside of Ultimaker websites. If you agree with the use of tracking cookies, click “I agree, continue browsing”. You can withdraw your consent at any time. If you do not consent with the use of tracking cookies, click “Refuse”. You can find more information about cookies on our Privacy and Cookie Policy page.
I made a similar object and sliced in 5.3.0 and mine slices correctly...I couldn't find any setting that would make it do that except maybe initial layer horizontal expansion. I would try to go back to default settings maybe uninstall/reinstall. Maybe the mesh is flawed or mesh correction is turned on and not right.. what if you put the model -0.2 mm on Z axis does it still do it? that might rule out flawed mesh. idk just some thoughts hope it helps let us know what happens!