Attached are a series of spectra of VV Cep covering 3800-4150A at R ~2500 (variable 3000-1500 across the range due to LHIRES chromatism)
Note the loss of H Balmer emission, broadening of the Ca II H K lines and relative drop in continuum flux below ~4000A, particularly noticeable in the latest spectrum recorded 2017-09-26
I saw the same changes in the similar system AZ Cas in 2012 as it entered eclipse and we lost the spectrum of the hot B star (Though there is no H Balmer emission in AZ Cas)
Chromatic Aberration. The inability of a lens to bring all wavelengths to focus in the same plane. The LHIRES uses an achromatic doublet which shows the usual pronounced chromatism in the Violet/UV so the focus varies across the spectrum.
Here is an updated plot including the latest spectrum from last night. There has been no further change in the past 9 days so it seems likely that the ingress phase is now complete at this wavelength.