There is lopa-substitution (elision) of the v and y when followed by any consonant except y,
The final व् or य् of any stem, be it a root or not, is elided by an affix &c, beginning with a वल् consonant i. e. any consonant except य् ॥ Thus दिव् + वस् 3.2.107 = दिव् + दिव् + वस् = दिदिवस् nominative singular दिदिवान्, दिदिवांसौ, दिदिवांसः ॥ Thus ऊय् + त = ऊतं, 'spun', क्नूय् + त = क्नूतं 'made a noise'. So also the affix ढ्रक् comes after गोधा in forming patronymic 4.1.129. Of the affix ढ्रक्, ढ is replaced by एय् 7.1.2. Thus गोधा + एय् + र = गौधेरः (the य् of the affix being even elided before र) ॥ So also in पचेरन्, यजेरन् the य् of लिङ् 3.4.102 is elided before रन् 3.4.105. So also व is elided in the following :-- from जीव् - जीरदानुः (by Unadi affix जीवे रदानुक्) from स्रिव् -अस्रेमाणम् formed by the Unadi affix मनिन् with the negative अ ॥ There being diversity in the application of Unadi affixes 3.3.1, there is not substitution ऊठ् for व् as required by 6.4.19.
Why do we say \before any consonant except य?\ Observe ऊय्यते, क्नूय्यते when य् is not elided. Why the word लोप is placed first? The elision of व् and ल् should take place prior to the elision of the aprrikta व् taught in the next sutra. Thus कण्डूय + क्विप् = कण्डू य् 6.4.48 = कण्डू + त् = कण्डूः ॥ So लोलूय + क्विप् = लोलूः ॥ \Why व् of व्रश्च is not elided before र् which is a वल् consonant? It is not elided, because it is so taught. Had the elision of व् been intended, the root would have been enunciated as रश्च instead of व्रश्च ॥ If you say the व is taught for the sake of forms like वृश्चति by samprasarana and वव्रश्च by reduplication, here also the 'lopa' would have applied, as being an Antaranga rule, while samprasarana, and the elision of र् by हलादिशेषः are Bahiranga.,