I had always experienced issues with previous compiles of ExChess. In fact it's a great engine developed by Dan Homan and it took part in TCEC events but it was unlucky under Android.
I hope with this brand new version compiled by Jim Ablett, a new engine can be introduced and show up in Rapidroid.
According to CCRL ranking, the PC version of ExChess running on 4 cores and 64-bit reaches 2880 ELO. Bearing in mind the gap from a PC down to Android increases when XB is used, my humble guess for ExChess can't be higher than 2600. Tests will tell the truth in any case unless the compile causes compatibility problems.
Please remember that JA wants all 3 files (engine, book, search.par) installed in the same folder in your device to get it running.
Download ExChess: HERE