Short Answer
The risk was minimal for a number of reasons, key among them being: (1) a divided political left (see SFIO) facing a basically unified centre-right, (2) firm political and military leadership from 1917, and (3) the increasing likelihood of victory on the battlefield, especially with the US entering the war made a revolution highly unlikely.
Also, the aims of the army mutineers of 1917 and the strikers in 1919-20 did not, except in isolated incidents, include demands for the overthrow of the political system.
DETAILS
Concerning the mutinies in the French army which started in May 1917, these were indeed serious and widespread, but were dealt with effectively and decisively by Petain who was appointed Commander-in-Chief on May 15th. In addition to “addressing the atrocious conditions in the trenches and reinstating a revised leave policy”,
Judicial courts-martial of targeted key offenders defused the most
outspoken resistance. A final phase allowed for the airing of
lingering grievances and a gradual return to order, as long as Pétain
kept his soldiers’ losses minimal through limited engagements...
...Instead of killing masses of insubordinate men, courts-martial
identified leaders, who were then punished and served as an example of
military justice at its highest level. Addressing the legitimate
grievances of the men, particularly through the intervention of junior
officers, allowed the time and space for morale to begin to
recover....
... in the end, French soldiers chose to obey orders and return to the
trenches, with a tacit agreement that no further futile offensives
would be launched.
Further, the mutinies in France did not take on a political dimension in the way that they did in Germany where the Kiel mutineers rapidly fanned out across Germany with demands for not just an end to the war but also a change in the political system. French mutineers were not demanding a change in the political system; they simply wanted better conditions in the trenches and an end to futile mass attacks against almost impregnable defensive positions.
France was on the winning side of the war. With American soldiers arriving in increasing numbers from June 1917 onwards, and with increasing numbers of British and French tanks being deployed, both French soldiers and civilians had good cause for optimism at a time when defeatism was spreading through the German army. Victory in a foreign war, especially a victory leading to the acquisition of territory, is rarely (if ever) fertile ground for a revolution.
Georges Clemenceau provided firm political leadership after being appointed Prime Minster in November 1917.
... from the outset, Clemenceau gave evidence of his firm
determination to revive the will to fight. He struck out against
defeatism, whether on the Right or the Left, and dealt directly with
trade union leaders with a mixture of coercion and improved
conditions.... Clemenceau's position waxed steadily stronger and was
never seriously in jeopardy in the chamber.
Source: Keith Robbins, The First World War
A key (though not the only) element in the collapse of the German will to fight was defeatism at the top level; this was in marked contrast to the attitudes of leaders in France and Britain. The French government skilfully trod a fine line between dealing with workers' (mostly financial) concerns and maintaining firm political control. In the election of November 1919, Clemenceau’s Bloc National won 412 of the 613 seats in the Chamber of Deputies.
There were divisions in the labour movement and the political left. In 1918, for example:
On 11 May Renault delegates voted for an immediate strike both for pay
and for the government to announce its war aims, a demand popular
among those opposed to an offensive war. Within two days the strike
spread to the Peugeot and Citroën plants to include a total of 200,000
workers. Strike rallies at Billancourt ended with cries of “Down with
war!”63 This unleashed the fury of the metal workers’ union with one
full-time official condemning the strike for putting the country at
risk in the context of a new German offensive. On 16 May the union
leaders gave an unconditional surrender to the new armaments minister;
Renault dismissed the strike leaders and 146 workers were sent to the
front.
Divisions in the working class were also evident on issues such as family allowances. As Paul Dutton in Origins of the French Welfare State (2002) says:
Employer control of family allowances and parliament’s consideration
of social insurance prompted rancorous debates within the working
class. Union leaders failed to stop the family allowance movement
because at virtually every turn they were confounded by divisions
among their own rank and file.
Further,
This division in the working class was exacerbated in 1919 with the
creation of a new union based on social Catholic ideals, the
Confédération Française des Travailleurs Chrétiens (CFTC). The
1920 Congress at Tours, where the French left split into rivaling
socialist and communist parties further fragmented the working class
on the question of social welfare.
Note:
The question seems to be partially based on a false premise – that Germany had to surrender because of the “fifth column of communists who were threat for stability of country”. This well-sourced Wikipedia article refutes this cause for the German defeat. Rather, the failure (after initial successes) of the German offensive led to the tide turning decisively from July 1918. Suffering from heavy losses and over-extended supply lines, and facing ever increasing numbers of newly-arrived American troops, the Germans were forced back and had little choice but to surrender.
Other sources
Sian Reynolds, France between the Wars: Gender and Politics (1996)
The Anatomy of Revolution
C. L. Mowat (ed) The Cambridge Modern History, vol XII: The Shifting Balance of World Forces, 1898-1945
Edward Shorter, Strikes in France 1830-1968
History of the French Communist Party