Arduino bluetooth HC-05 servo control
When using

if(BT.available())


that's doing the same as

if(BT.available() &gt; 0)


But then you are reading 2 bytes, though you cannot be sure, that there are 2 bytes to read. The data is transmitted serially, so even when you send it on your phone in one bunch, it does not get transmitted as bunch.

Try to use

if(BT.available() &gt;= 2)


Also makes sure, that nothing else gets send over serial besides the numbers (often there is a line ending send implicitly depending on the used app).