The speakers you have encoutered may be adding Erhua which is common in the Beijing dialect of Mandarin.
The '-er' that is added serves various semantic purposes (e.g. diminutive suffix) and is considered standard in PRC issued education and examination guidelines for the Standard Chinese (Mandarin) language. It is possible that the speaker is instinctively using erhua when they intend to communicate a similar modification of idea while speaking English.
"even before a consonant"
In Mandarin, syllables are constructed of initials, finals, and a tone. The next initial (following consonant) doesn't affect the pronunciation of finals. See Pinyin.
Assuming that the final ɹ you are hearing is unique to something about the Chinese language, it is unlikely that the following consonants would affect the habit.
Li, Charles N., and Sandra A. Thompson. “Word Structure, 3.2.1 Affixation, C.1 -er.” Mandarin Chinese: A Functional Reference Grammar, University of California Press, 1989, pp. 39.