Acording to the aeropress-bg.com website, this happend last december:
The fleet of the Su-25 ground attack jets of the Bulgarian Air Force is grounded due to depletion of their interdependent resources. The last type flights were completed on December 14, 2017 in Bezmer.
The webpage confirmed that only a few Su-25 were airworthy in the last year, and altough the Defence Ministry talked about a possible modernisation of the Su-25 and the MiG-29, as of today that not happend. The aeropress-bg.com site also mentions, there are plans that 6 to 8 Su-25 might get an overhaul:
the possibility that several (six to eight) Su-25 airplanes will be sent to the KPU in Belarus, more precisely at the 558th Aircraft Repair Plant in Baranovichi. It is possible, at least in theory, to implement the LR in Ukraine (MIGremont Plant in Zaporozhye), Russia (121 APZ in Cubanka) or Georgia (TAM plant).