[REGRESSION] Missing icon toolbars

Requirements

• I searched through the issues if the issue already exists

Steps to reproduce

1. Launch LabPlot.
2. Click on "Project" in the Project Explorer.

Expected

The icon toolbar is displayed.

Observed

The icon toolbar is not displayed. The icon toolbar seem to be incomplete also for other objects (e.g. the missing "Save" if a spreadsheet is shown) . This happens occasionally.

Labplot Version

Debug build 
System: Ubuntu 23.04
Locale: English,United States (Decimal point ',', Group separator ' '
Number settings: Decimal point ',', Group separator ' ', Exponential 'e', Zero digit '0', Percent '%', Positive/Negative sign '+'/'-' (Updated on restart)
Architecture: x86_64-little_endian-lp64
Kernel: linux 6.2.0-32-generic
C++ Compiler: GNU 12.3.0
C++ Compiler Flags: -g -O2 -fdebug-prefix-map=/build/labplot-rvXKyy/labplot-2.10.1+git202309101633~ubuntu23.04.1=. -flto=auto -ffat-lto-objects -fstack-protector-strong -Wformat -Werror=format-security -Wdate-time -D_FORTIFY_SOURCE=2 -fno-operator-names -fno-exceptions -Wall -Wextra -Wcast-align -Wchar-subscripts -Wformat-security -Wno-long-long -Wpointer-arith -Wundef -Wnon-virtual-dtor -Woverloaded-virtual -Werror=return-type -Werror=init-self -Wvla -Wdate-time -Wsuggest-override -Wlogical-op -Wall -Wextra -Wundef -Wpointer-arith -Wunreachable-code -Wunused -Wdeprecated-declarations -fno-omit-frame-pointer -fstack-protector -fexceptions -std=c++17 -O2 -Wcast-align -Wswitch-enum -fvisibility=default -pedantic -Wzero-as-null-pointer-constant