diff --git a/srsue/src/test/ttcn3/hdr/lte_ttcn3_phy.h b/srsue/src/test/ttcn3/hdr/lte_ttcn3_phy.h
index 6a38708ba..e262855e8 100644
--- a/srsue/src/test/ttcn3/hdr/lte_ttcn3_phy.h
+++ b/srsue/src/test/ttcn3/hdr/lte_ttcn3_phy.h
@@ -119,8 +119,8 @@ private:
 
   int prach_tti_tx = -1;
 
-  int  sr_tx_tti  = -1;
-  bool sr_pending = false;
+  std::atomic<int32_t> sr_tx_tti  = {-1};
+  std::atomic<bool>    sr_pending = {false};
 
   std::mutex phy_mutex;
 
diff --git a/srsue/src/test/ttcn3/hdr/ttcn3_syssim.h b/srsue/src/test/ttcn3/hdr/ttcn3_syssim.h
index 1c18195d7..667ae210d 100644
--- a/srsue/src/test/ttcn3/hdr/ttcn3_syssim.h
+++ b/srsue/src/test/ttcn3/hdr/ttcn3_syssim.h
@@ -276,7 +276,7 @@ private:
   std::vector<unique_syssim_cell_t>      cells;
   int32_t                                pcell_idx = -1;
 
-  // Main mutex to protect access from syssim's main thread (epoll handlers) and calls from  UE's stack thread
+  // Main mutex to protect access from syssim's main thread (epoll handlers) and calls from UE's stack thread
   std::mutex syssim_mutex;
 
   // Internal function
diff --git a/srsue/src/test/ttcn3/src/ttcn3_dut.cc b/srsue/src/test/ttcn3/src/ttcn3_dut.cc
index f50e2d64a..46cb23733 100644
--- a/srsue/src/test/ttcn3/src/ttcn3_dut.cc
+++ b/srsue/src/test/ttcn3/src/ttcn3_dut.cc
@@ -105,7 +105,7 @@ all_args_t parse_args(ttcn3_dut_args_t* args, int argc, char* argv[])
   all_args.stack.log.gw_hex_limit   = args->log_hex_level;
   all_args.stack.log.usim_hex_limit = args->log_hex_level;
 
-  all_args.stack.sync_queue_size = 1;
+  all_args.stack.sync_queue_size = MULTIQUEUE_DEFAULT_CAPACITY;
 
   return all_args;
 }
diff --git a/srsue/src/test/ttcn3/src/ttcn3_syssim.cc b/srsue/src/test/ttcn3/src/ttcn3_syssim.cc
index 71c92cfca..6c689345e 100644
--- a/srsue/src/test/ttcn3/src/ttcn3_syssim.cc
+++ b/srsue/src/test/ttcn3/src/ttcn3_syssim.cc
@@ -248,8 +248,8 @@ void ttcn3_syssim::new_tti_indication(uint64_t res)
 
   // DL/UL processing if UE has selected cell
   dl_rnti = ue->get_dl_sched_rnti(tti);
-  if (SRSRAN_RNTI_ISSI(dl_rnti)) {
-    // deliver SIBs one after another
+  if (SRSRAN_RNTI_ISSI(dl_rnti) && (tti % 2 == 0)) {
+    // deliver SIBs one after another in every other TTI
     mac_interface_phy_lte::mac_grant_dl_t dl_grant = {};
     dl_grant.tti                                   = tti;
     dl_grant.pid                                   = get_pid(tti);
@@ -257,7 +257,7 @@ void ttcn3_syssim::new_tti_indication(uint64_t res)
     dl_grant.tb[0].tbs                             = cells[pcell_idx]->sibs[cells[pcell_idx]->sib_idx]->N_bytes;
     dl_grant.tb[0].ndi                             = get_ndi_for_new_dl_tx(tti);
     ue->new_tb(dl_grant, cells[pcell_idx]->sibs[cells[pcell_idx]->sib_idx]->msg);
-    logger.info("Delivered SIB%d for pcell_idx=%d", cells[pcell_idx]->sib_idx, pcell_idx);
+    logger.info("Delivered SIB%d for pcell_idx=%d", cells[pcell_idx]->sib_idx + 1, pcell_idx);
     cells[pcell_idx]->sib_idx = (cells[pcell_idx]->sib_idx + 1) % cells[pcell_idx]->sibs.size();
   } else if (SRSRAN_RNTI_ISRAR(dl_rnti)) {
     if (prach_tti != -1) {