We have examined three plausible explanations for the HFF14Spo events: (1) they were separate rapid outbursts of an LBV star, (2) they were surface explosions from a single RN, or (3) they were each caused by the rapidly changing magnification as two unrelated massive stars crossed over lensing caustics. We cannot make a definitive choice between these hypotheses, principally due to the scarcity of observational data and the uncertainty in the location of the lensing critical curves.

If there is just a single critical curve for a source at \(z=1\) passing between the two HFF14Spo locations, then our preferred explanation for the HFF14Spo events is that we have observed two distinct eruptive episodes from a massive LBV star. In this scenario, the HFF14Spo LBV system would most likely have exhibited multiple eruptions over the last few years, but most of them were missed, as they landed within the large gaps of the HST Frontier Fields imaging program. The HFF14Spo events would be extreme LBV outbursts in several dimensions, and should add a useful benchmark for the outstanding theoretical challenge of developing a comprehensive physical model that accommodates both the \(\eta\,\mbox{Car}\)-like great eruptions and the S Dor-type variation of LBVs.

If instead the MACS0416 lens has multiple critical curves that intersect both HFF14Spo locations, then the third proposal of a microlensing-generated transient would be preferred. Stellar caustic crossings have not been observed before, but the analysis of a likely candidate behind the MACSJ1149 cluster\citep{Kelly:2017} suggests that massive cluster lenses may generate such events more frequently than previously expected\citep{Kelly:2017, Diego:2017}. To resolve the uncertainty of the HFF14Spo classification will require refinement of the lens models to more fully address systematic biases and more tightly constrain the path of the critical curve. High-cadence monitoring of the MACS0416 field would also be valuable, as it could catch future LBV eruptions or microlensing transients at or near these locations.