p2p: Add warning message when receiving headers for blocks cached as invalid

diff --git a/src/net_processing.cpp b/src/net_processing.cpp
index 9cab2461..c539f4a5 100644
--- a/src/net_processing.cpp
+++ b/src/net_processing.cpp
@@ -2955,6 +2955,13 @@ void PeerManagerImpl::ProcessHeadersMessage(CNode& pfrom, Peer& peer,
                                                            state, &pindexLast)};
     if (!processed) {
         if (state.IsInvalid()) {
+            if (!pfrom.IsInboundConn() && state.GetResult() == BlockValidationResult::BLOCK_CACHED_INVALID) {
+                // Warn user if outgoing peers send us headers of blocks that we previously marked as invalid.
+                LogWarning("%s (received from peer=%i). "
+                           "If this happens with all peers, consider database corruption (that -reindex may fix) "
+                           "or a potential consensus incompatibility.",
+                           state.GetDebugMessage(), pfrom.GetId());
+            }
             MaybePunishNodeForBlock(pfrom.GetId(), state, via_compact_block, "invalid header received");
             return;
         }
diff --git a/src/validation.cpp b/src/validation.cpp
index 73b3e91d..e1d6babf 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -4244,7 +4244,8 @@ bool ChainstateManager::AcceptBlockHeader(const CBlockHeader& block, BlockValida
                 *ppindex = pindex;
             if (pindex->nStatus & BLOCK_FAILED_MASK) {
                 LogDebug(BCLog::VALIDATION, "%s: block %s is marked invalid\n", __func__, hash.ToString());
-                return state.Invalid(BlockValidationResult::BLOCK_CACHED_INVALID, "duplicate-invalid");
+                return state.Invalid(BlockValidationResult::BLOCK_CACHED_INVALID, "duplicate-invalid",
+                                     strprintf("block %s was previously marked invalid", hash.ToString()));
             }
             return true;
         }