  We have characterized 26 Spitzer/IRAC-selected sources from the SMUVS program
that are undetected in the UltraVISTA DR5 H- and/or Ks-band images, covering 94
square arcmin of the COSMOS field which have deep multiwavelength JWST
photometry. We analyzed the JWST/NIRCam imaging from the PRIMER survey and
ancillary HST data to reveal the properties of these galaxies from spectral
energy distribution (SED) fitting. We find that the majority of these galaxies
are detected by NIRCam at <2 micron, with only four remaining as near-infrared
dropouts in the deeper JWST images. Our results indicate that the UltraVISTA
dropouts candidates are primarily located at z>3 and are characterized by high
dust extinctions, with a typical color excess E(B-V) = 0.5 pm 0.3 and stellar
mass log(M*/Msun) = 9.5 pm 1.0. Remarkably, ~75% of these sources show a flux
enhancement between the observed photometry and modeled continuum SED that can
be attributed to Halpha emission in the corresponding NIRCam bands. The derived
(Halpha+ N[II] + S[II]) rest-frame equivalent widths and Halpha star formation
rates (SFRs) span values ~100-2200 A and ~5-375 Msun/yr, respectively. The
location of these sources on the SFR-M* plane indicates that 35% of them are
starbursts, 40% are main-sequence galaxies and the remaining 25% are located in
the star-formation valley. Our sample includes one active galactic nucleus and
six submillimeter sources, as revealed from ancillary X-ray and submillimeter
photometry. The high dust extinctions combined with the flux boosting from
Halpha emission explain why these sources are relatively bright Spitzer
galaxies and yet unidentified in the ultradeep UltraVISTA near-infrared images.
