This common Indy problem has popped up again for me with Lazarus 1.8 RC2...
While compiling twice works fine, but actually trying to install it afterwards still fails and results in:
Warning: Recompiling IdStreamVCL, checksum changed for IdGlobal
IdStream.pas(29,3) Fatal: Cannot find IdStreamVCL used by IdStream, incompatible ppu=D:\installed components\Indy_lazarus\Lib\lib\x86_64-win64\IdStreamVCL.ppu, package indylaz
Not sure how to solve this as the solutions I usually used do not appear to work.... Any ideas what to check?