Here is an example where r occurs before vowels:
The shelter of your arms, Mother Earth
I'm referring to this service for transcription.
British transcription shows that none of them are silent:
ðə ˈʃɛltər əv jər ɑːmz, ˈmʌðər ɜːθ
This conforms to how first TTS engine installed on my system pronounces it, there are 3 linking rs.
While second TTS engine has only 1 linking rs, it sounds more like:
ðə ˈʃɛltə əv jər ɑːmz, ˈmʌðə ɜːθ
I considered the lack of linking r between shelter and of unnatural, but I could be wrong. And I'm not sure about Mother Earth, it didn't sound wrong without linking r.
Did second engine get it wrong? Should all of these linking r's be pronounced as a rule of thumb? Considering that no logical pause between words is intended (e.g. punctation), is it acceptable for r to be silent before vowels and what are those cases?
I primarily refer to Standard British English but if there are acceptable variations, I would like to know about them.