2735221 - Detected damaged column with error 'ridmap or mergemap region overlapped' & s_dpidx.cxx:7549 in IQ16.0 SP11.20 -- SAP IQ

Due to the risk of Data Corruption with SP11.21, customer downgraded IQ server from 'sp11.21' to 'SP11.20' 
by the instruction from note 2734980.  After restarting with SP11.20, several ETL jobs failed due to "Non-Fatal IQ Internal Error" 
with "ridmap or mergemap region overlapped" message.
   
It's not sure whether the problem column was damaged on SP11.21 or  corruption affected on sp11.20.
DBCC with allocation mode reported 'No Error Detected', however DBA done rebuild index on problem column and customer batch was completed well.

   ** .iqmsg & stacktrace
      ...
      [20897]:    10000000 Rows, 5 Seconds
      barray t140299915421440 XXXX: CheckColumnEBMCoverage
      barray t140299915421440  *** REGION OVERLAP, curKey=5434561,5450936] curRidmap=[5450881,5467200]
      ...
      barray t140299915421440 C4 BEGIN dump RidMap:
      barray t140299915421440 C4 startRecid=5124481 endRecid=5140800 block=1223 hasNBit=0
      ...
      barray t140299899631360 C17 END dump RidMap
      t140299899631360 *** DB.XXXX.ASIQ_IDX_XXX_INDEX (datetime): ridmap or mergemap region overlapped.
      ...
      **       Non-Fatal IQ Internal Error Detected
      **       at slib/s_dpidx.cxx:7548  on thread 140299918579456 (TID 1087)
      ...
      **       End of stack trace from Non-Fatal IQ Internal Error slib/s_dpidx.cxx:7549

      '''
      ===== Thread Number  140299899631360  (IQ connID: 0000000466) =====
       .. pcstkwalk
       .. ucstkgentrace
       .. StackTraceForThisThread
       .. hs_ThrowIdxException
       .. hs_dp::CheckIndexConsistency
       .. hs_dpInsert::Complete
       .. dfiio_FP::PostFetchOpus
       .. dfo_IndexInsert::PostFetchOpus
       .. df_CombinerFinalFetchHelper::ExecWork
       ...
       ...

SAP IQ 16.0 SP11 PL21

s_dpidx , "ridmap or mergemap region overlappe" , CheckColumnEBMCoverage , RidMap , CheckIndexConsistency, , KBA , BC-SYB-IQ , Sybase IQ , Bug Filed