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We present SN 2019tsf (ZTF19ackjszs) and SN 2019oys (ZTF19abucwzt). These twostripped envelope Type Ib supernovae suddenly showed a (re-)brightening intheir late light curves. We investigate this in the context of circumstellarmaterial (CSM) interaction with previously ejected material, a phenomenon thatis unusual among SE SNe. We analyse observational data, consisting of opticallight curves and spectra. For SN 2019oys we also have detections in radio aswell as limits from UV and X-rays. Both light curves show spectacularre-brightening after about 100 days. In the case of SN 2019tsf, there-brightening is followed by a new period of decline, and the spectra nevershow signs of narrow emission lines that would indicate CSM interaction. On thecontrary, SN 2019oys made a spectral makeover from a Type Ib to a spectrumclearly dominated by CSM interaction at the light curve brightening phase. Deepspectra reveal a plethora of narrow high ionization lines, including coronallines, and the radio observations show strong emission. The rather similarlight curve behaviour indicate CSM interaction as the powering source. For SN2019oys the evidence for a phase where the ejecta hit H-rich material, likelyejected from the progenitor star, is conspicuous. We observe strong narrowlines of H and He, but also a plethora of high ionization lines, includingcoronal lines, revealing shock interaction. Spectral simulations of SN 2019oysshow two distinct density components, one with density > 1e9/cm3, dominated bysomewhat broader, low ionization lines of H I, He I, Na I and Ca II, and onewith narrow, high ionization lines at a density about 1e6 /cm3. The former isstrongly affected by electron scattering. The evidence for CSM interaction inSN 2019oys is corroborated by detections in radio. On the contrary, for SN2019tsf, we find little evidence in the spectra for any CSM interaction.

Two stripped envelope supernovae with circumstellar interaction -- but only one really shows it